According to the Realists, war is essential for serving its interests as for war is mean to achieve their national interests. The institution of war has evolved with the development of state after the peace of Westphalia which gives state supreme power to exercise within its boundaries without inferring in internal matters of the other states.
According to Clausewitz war is a continuation of politics by other means. The industrialization played a vital role in promoting war by developing new weapons and revolutionizing the institution of war. It was in eighteen century when war becomes a proper institution which is equipped with modern weapons and tactics. Alexis de Tocqueville concluded that war almost always enlarges the mind of a people and raises their character.” Kenneth Waltz defines war as “The ultimate resort of states that can see no other way to have their interests met.” Moreover, War was used as a tool by states to expand its territory and area of influence since ancient times like Athens fight against Spartan to control them.
In the twentieth century, the fascination for war is declining especially after the experience of WWI and almost all the countries of the developed world committed to avoiding war between states. The deterrence was also used by states to prevent war by equipping them with arms to teeth to deal with the aggressive states.  However, this policy failed with the start of WWII but with the start of a cold war between US and USSR did bring stability by changing of international structure from multi-polarity to bi-polarity. Both powers avoided direct confrontation and the world was divided into two blocs. Kenneth Waltz declared Bi-polar system as a most stable system because both powers tried to balance each other power which reduces the chances of war.
Merits of Bi-polarity
Similarly, nuclear weapons also played a significant role in averting war as both powers acquired nuclear weapons. Kenneth Waltz called nuclear weapons as an effective tool to prevent war between US and USSR as the use of nuclear weapons after 1945 become unthinkable for any state due to its destructive ability. According to experts, Bi-polarity proved to be a more balanced system as it would not allow one state to dominate all other states of the world. Bi-polarity created a balance between two potential powers and brings stability at international level as both were equally capable of competing with other. Both states balanced each other power by created two blocs to check each other growing power at global level.
Arguments in favor of Obsoleteness of War
1- Economic Integration
The interdependence of economy is considered as a major development which is preventing the war, especially between states. For Instance, in the case of China and US despite their rivalry, there is less likely chance of war between both the states. War creates instability and disrupts the economy in a negative way by causing inflation. The international economic system has increased the dependence of states irrespective of their size. The economic integration among states is not allowing them for waging war because it is not cost effective for a state. In contemporary world war is undesirable and becoming a burden on the economy of the country.
In the case of China and US relations although they are competing with each other but they would not use war as a tool to increase their influence in the global arena. Since war is not a viable option to pursue their national interests. Similarly, China is suspicious of an American presence in the Asia-Pacific region and their growing ties with its neighboring states. One cannot say that they will be involved in direct confrontation with each other. Since economic interests of the both states are inter-linked and mutually dependent upon each other. China is the biggest trading partner of US and a major importer of Chinese products. In addition, globalization played a vital role in increasing the interdependence between the states by linking all states with the common economic system and its stability is dependent upon the cooperation among all states of the world. Globalization has transformed the world into the global village by inter-linking world trade.
2- Role of international organization
The role of the international organization is significant in preventing war between states by including all states into organizations to resolve their issues by using the dialogue process and building the mutual consent of all the states of the world. International organization provides a platform to resolve the contentious issues by negotiation rather going for war as a mean to sort out their conflictual issues between the states. Moreover, legislation of international organization is very effective in averting war between states as they punished those who are involved in crimes against humanity in the form of ethnic cleansing and genocide in Rwanda and Yugoslavia.
Furthermore, international organizations are effective in ending conflicts between the states by providing a platform and giving importance to objections of the both parties. International organizations play a mediating role to resolve issues between states by hearing both parties and suggesting ways to sort the contentious issues between any two or more states. In addition, regional organizations have improved the regional integration by dealing the regional problems with regional players. For example, European Union is the most successful organization which has united Europe by resolving their issues internally and consider as a most stable region of the world. The European Union is an effective regional organization which makes it most peaceful part of the world as they sort their issues by discussing with each other.
3- Cost of WAR
The cost of war outweighs its benefits for the state as it long-lasting effects on its people. The advancement in modern weapons has increased the destructive abilities of war by causing infrastructure losses for the state. In contemporary world states prefer to avoid war due its interdependence on other states for trade and for proper functioning relations with its neighbors. Similarly, the human cost of war is another factor which is becoming a reason for preventing wars between the states. The use of chemical and biological weapons in modern warfare has increased the number of deaths of humans within the second that is mostly avoided by the countries.
Moreover, the signing of treaties by almost all states of the world to limit the number of conflicts is another factor to discourage countries from using force against any other country. In addition, war drains the economy of a country and creates dissatisfaction at the domestic level. For example, during the Vietnam War US had to stop war due to protests within the country against War due to its effects on their domestic economy. The economic cost of wars in the contemporary world has played a major role in preventing a war between the states. War is not considered as the viable option for states to pursue their national interests.
4-Use of non-military means
The use of non-military means by the states is another major reason towards decline war in 21 century. The states tend to use other means for instance; cyber warfare is widely used by China and US to keep a check on their growing power. The countries in contemporary world avoid using force against other states because it is not cost effective for them. Cyber warfare is not only cost effective for states but also a viable option to pursue their interests without heavy spending on its defence. Moreover, cyber warfare would cause more damage to the rival states without indulging in direct confrontation with the other states.
The hacking incidents in the past few years have increased and hackers usually hacked national websites to the country to get access to countries confidential documents and their assets to expose the ability of the state. Cyber warfare is cost effective mean used by countries to subdue their rival states. The modern technological advancement has increased the role of cyber warfare as all systems of the world are dependent on the digital means. Moreover, computer viruses are also used by almost all states to destroy the confidential projects of their rival states without much effort and violating international laws against the use of force at the global level.
5- Nuclear weapons
Nuclear weapons have also played a significant role in preventing war between states because of its destructive nature and long-lasting effects on the humans and living beings. Nuclear weapons are considered as psychological weapons or political weapons that act as a deterrent to prevent war between the two or more states. The development of nuclear technological has changed the nature warfare to a greater extent by reducing chances of War Between the States. During cold war nuclear weapons prevented the direct confrontation between US and USSR. The use of nuclear weapons by either by US or USSR would ensure mutual destruction of both the states.
The use of nuclear weapons is not an acceptable norm at international due to destructive ability to destroy humans indiscriminately. It is considered as taboo by responsible states and international community because of its negative repercussions on the humanity. They are used prevent War among the States. International norms against the use of nuclear weapons have played the significant role in avoiding conflict between the states and acts as a deterrent to states.
According to some experts, war is not obsolete in the contemporary world rather it has transformed the old warfare. The institution war has become more organized and lethal. The modern technology has revolutionized the nature warfare by equipping states with modern weapons. The decline of war as an institution is not easy to achieve with growing insecurities of the states. States are facing security dilemma and in order to compete with other states every state is increasing their defense budget to ensure their security. Similarly, change in international structure from Uni-polarity to Multi-polarity is another reason why states are investing more to improve their military capacity to compete for more than one power at international level.
Moreover, experts are of the view that nuclear weapons are not preventing war instead they are increasing the military disparities between the states. The countries who acquire nuclear weapons after the 1950s are competing with P-5 by developing Tactical Nuclear weapons. They are also known as mini-nukes basically these low-intensity nuclear weapons which are increasing chances of war among the states. The accidental use of tactical weapons can start a war due to growing distrust among major countries of the world. For example, in a case of India and Pakistan, accidental use of tactical nuclear weapons can initiate a war between these two states.
If we analyzed arguments in favor of the obsoleteness of war are based on logical argumentation and empirical evidence. It would be plausible to say that institution of war is facing a decline due to growing awareness among general public and policy makers. War is not cost-effective and becoming a burden on economies of the countries. Similarly, modern weapon technologies have increased the defence budget rather spending this money to eradicate poverty and violence in the world. Moreover, development of nuclear weapons is also contributed in preventing war because the use of nuclear weapons can kill thousands of people within seconds especially after witnessing the example of Nagasaki and Hiroshima in 1945.
Despite differences among states they give importance to the process of dialogue to resolve their conflictual issues rather than going for war. The cost of war out weights the benefits of war if we assess the implications of war for humans it would be safe to claim that war cause more problems for people who have to face the consequences of war in the form of loss of their lives and displacement from their respective countries to neighboring areas. It would be plausible say that war between states is obsolete if not within the states. The conflicts within the countries are there but it can be addressed by using dialogue process and giving autonomy to minority groups in the countries.
If we compare and contrast arguments in favor and against of war one can say that war is considered as the only option for states in resolving their issues with other states. The institution of war is facing decline after the conclusion of the two World Wars. War is not used by states to protect their national interests due to its heavy cost in the form of both human and material cost of the war. Globalization has also played significant role limiting the role of War at international level by promoting interdependence among all states of the world. Furthermore, war itself causes more problems rather than resolving contentious issues between the countries.
The increasing economic interdependence among states has decreased chances of war as their economic interests are interlinked. War is expensive for any state since it requires not only man-power but also the economic power to sustain the war for a long time. The countries having viable economies if they start a war consequently it will drain their economy and create issues within their states. The economic integration of regions has paved the way in preventing war between states by bringing stability and prosperity to all states irrespective of their relative power capabilities.
Social constructivism theory is presented by Nicholas Onuf, Alexander Wendt, Emanuel Adler, Friedrich Kratochwil, John Gerard Ruggie and Peter Katzenstein. According to proponents of the social constructivism international structure is socially constructed with interactions of human with each other. States objective goals in the form of security and economic development and subjective goals their international standing are created by their interactions with other actors of the world. States identities and interests are constructed from inter-subjective social structures because global actors interact with each other to formulate their interests by comparing them with other states. The identities and interests of actors are socially constructed by their interaction with each other.
According to constructivists anarchy is not given rather it is socially constructed with interactions of global actors. If all states are interacting in a peaceful manner then it is peaceful and if the country suspects each other intentions then it is conflictual in nature. In simple words, it depends on upon the interactions of the global actors with each other. Constructivist negates realist assumption about anarchy that it is given. It is constructed by an interaction of global actors and it changes the behavior of global actors. The interest of the states keeps on changing with a change in international structure as they are stagnant or permanent.
The international system is not given or present like the solar system. It is constituted by inter-subjective interaction among the people. The international system is constructed with the ideas that are not based on the objective reality. Social Constructivism is based upon the set of ideas, norms of people living in a particular area. According to the constructivists understanding the meanings of ideas and concepts is significant because it is based on interactions human with other by comparing them with each other.
In the case of relations with China and US one can say they experienced ups and downs with the changing nature of their national interests.  During the 1950s, the relations between both the states were conflictual in nature due to American involvement in Korean Peninsula and their support for Nationalist Taiwan. In the 1970s during Nixon Presidency, US tried to normalize their relations by visiting China and accepted People Republic China (PRC) legitimacy using Ping Pong by sending their table tennis team to China. The shift in relations occurred due to changing nature of their national interest and abandons the Nationalists of Taiwan. The US normalized their relations with China to curtail the Russian expansion in the region and increase American area of influence in the Asia-Pacific region.
If we analyzed the relations of the both countries using the Social Constructivists lens one can say China and US have experienced a period of strained relations and normal relations depending upon the nature of interests that are changing with a shift in the international system. It is either peaceful or conflictual in nature. Moreover, in recent past, the increased in economic interdependence has improved their relations with each other due to dependence upon each other for achieving their economic interests. Similarly, China and the USA are competing with other economically due to growing Chinese economy and rise as a major player at international level. China and USA are suspected of each other activities particularly in the Asia-Pacific region due to growing Chinese influence in the region.
The relations between China and US are largely driven by their distinct ideologies and identities. The foreign policy of both of these countries is dependent on their identities which are different from each other. The understanding of their respective identities is essential for making sense of their posture towards each other. States acts according to national interests that are based on their identities. According to Social Constructivism understanding of identities is required to analyze the relations between two states in detail. The role of identities is significant is determining the major policy decisions that are largely dependent upon the ideational factors of the state.
In the context of China and US, the role of the identity cannot be undermined because both give importance to their identities in their relations with each other. The in-depth understanding of the foreign policies of China and US is largely based on their distinct identities. The nature of the relationship between China and US is very complex due to the vital role of their respective identities in their major policy decisions towards each other. China gives importance to its identity in the conduct of their relations with US and rest of the world. In the same way, the US also promotes democracy at the international level that signifies the role of identity in their foreign policy.
To conclude, war is obsolete particularly between the states in the contemporary as no major war is fought between states. The institution war is facing a decline due to its heavy cost paid the people. The countries prefer to use non-military means to increase their sphere of influence rather using force to get their interests. The phenomena of war are not fascinating for young people anymore as it used to be in past. The repercussions of war have far-reaching effects on the humans by disturbing them emotionally and mentally. Moreover, nuclear, biological and chemical weapons are another factor which is vital for averting war among the states due to its implications for humans. The countries at international level do not promote war to solve their conflictual issues with each other. The international organizations are effective in ending the war between states by promoting peace and stability. Similarly, the role of effective civil society and epistemic communities cannot be undermined in preventing war at a global level. The epistemic community has played a vital role in stigmatizing the use of nuclear, chemical and biological weapons.
Lastly, war is not considered by states as an only option to pursue their national interests as it used to be in the 17th and 18th century. Realist school of thought promoted war as tool or Lastly, no doubt war is not considered by states as an only option to pursue their national interests as it used to be in the 17th and 18th century. Realist school of thought promoted war as a tool or mean by states to achieve their national interests. In 21 century the role war is not vital due to increasing in economic interdependence between the states. The economic integration at the regional level is important in ending major conflicts among states of the particular region. War as an institution is not effective at international due to a shift of countries towards non-military means to subdue their rivals rather than indulging them in war or military confrontation with each other.
Hans G. Brauch, "The Three Worldviews of Hobbes, Grotius and Kant Foundations of modern thinking on peace and security Contextual Change and Reconceptualisation of Security," AFES-PRESS, accessed June 5, 2016, http://www.afes-press.de/pdf/Hague/Brauch_Worldviews.pdf.Sherpa Subirana, "Is War Becoming Obsolete in International Affairs? Discuss with Reference to the Academic Debate on the Issue. | Lobsang Dundup Sherpa Subirana - Academia.edu," Academia.edu - Share Research, accessed June 5, 2016, https://www.academia.edu/6647109/Is_war_becoming_obsolete_in_international_affairs_Discuss_with_reference_to_the_academic_debate_on_the_issue. John Mueller, "IS WAR STILL BECOMING OBSOLETE?," Political Science | OSU, last modified August 3, 2012, http://politicalscience.osu.edu/faculty/jmueller/apsa1991.pdf. Rosella Cappella, "Confronting the Cost of War: The Political Economy of War Finance | Center for Finance, Law & Policy," Boston University, accessed June 5, 2016, http://www.bu.edu/bucflp/initiatives/confronting-the-cost-of-war-the-political-economy-of-war-finance/ Terry L. Deibel, "Foreign Affairs Strategy - Cambridge University Press," Home | Cambridge University Press, accessed June 5, 2016, https://www.cambridge.org/catalogue/catalogue.asp?isbn=9781107453302&ss=exc. Kenneth Waltz, "Kenneth Waltz, The Spread of Nuclear Weapons: More May Better, Adelphi Papers, Number 171 (London: International Institute F," Mount Holyoke College, last modified 1981, https://www.mtholyoke.edu/acad/intrel/waltz1.html. Roya J. Amineh and Hanieh D. Asl, "Review of Constructivism and Social Constructivism," Journal of Social Sciences, Literature and Languages 1, no. 1 (April 2015): xx, Available online at jssll.blue-ap.org. Hui Wang, "U.S.-CHINA: BONDS AND TENSIONS," RAND Corporation Provides Objective Research Services and Public Policy Analysis | RAND, accessed June 5, 2016, https://www.rand.org/content/dam/rand/pubs/monograph_reports/MR1300/MR1300.ch12.pdf Yan Xuetong, "The Instability of China-US Relations," The Chinese Journal of International Politics 3, no. 3 (2010): xx, doi:10.1093/cjip/poq009.