If there is one issue which will determine the future course of the 21st century, it is the direction and substance of US-China relations in the coming decades. The driving factors behind this relationship are twofold: the US determination to prevent the emergence of a power in any part of the world capable of challenging its global supremacy and the phenomenal economic growth of China over the past three decades which in due course would translate itself in the growth and strength of its military power. The combined effect of Chinas huge size and rapid growth makes it inevitable that the world would, at first, see increasing rivalry between the two nations in the economic field followed by a challenge to the US global supremacy in the military field by China in the second half of the 21st century. Of course, this conclusion is based on the bold assumption that the present trends of growth in the economic power of the two nations are sustained in the coming decades. These developments would transform the global geopolitical scene with far-reaching strategic, political and economic implications for the whole world. There is no denying the fact that the current world order has been shaped primarily by the West under the leadership of the US - a reflection of the Western countries domination of the global political and economic scene since the end of the World War II. The structure, the procedures and the functioning of the United Nations, particularly the Security Council, the World Bank and the IMF, established after the World War II, were such that no major decision could be taken without the backing of the West. The position has remained more or less unchanged since then. This state of affairs is going to change dramatically in the coming decades reflecting the redistribution of the economic and ultimately the military power globally. During the Cold War, the Soviet Union did pose a challenge to the military supremacy of the West. The defeat and disintegration of the Soviet Union made the world unipolar briefly with the US emerging as the global hegemon. However, the rapid growth of China and other powers like India and Brazil, the re-assertiveness of Russia, and the emergence of other power centres such as the European Union, Japan and the ASEAN indicate that the US unipolar moment has already passed. The world is increasingly turning multipolar with several centres of power emerging on the scene even though for the time being the US is the only country capable of projecting its military power in the different corners of the world. It is inevitable that these developments would ultimately lead to the re-writing of the rules which determine the way in which the world functions in the political and economic fields. Chinas rapidly growing economic and military strength would make it a major player in this process of global transformation. An example of the kind of changes that can be expected in the coming decades was the call by the Governor of Chinas Central Bank, Zhou Xiaochuan, in March 2009 for the replacement of the dollar as the worlds reserve currency by Special Drawing Rights (SDRs). Changes can, thus, be expected in the structure and functioning of multilateral institutions like the UN Security Council, the World Bank, the IMF and the WTO. The net effect of these changes would be the gradual decline in the influence of the US and the West and increase in the role of China and other emerging powers. The changes in the structure and functioning of the international political and economic institutions will be only one consequence of the growing rivalry between the US and China. There will also be important consequences of this development for US-China bilateral relations. The US-China relationship is both cooperative and competitive at present. China is an extremely important trading partner of the US. In 2008, Chinas exports to the US were estimated to be $338 billion whereas its imports from the US amounted to $70 billion. China is also the recipient of the US private investment on a large scale. Many US firms have established their manufacturing facilities in China which has thus also benefited from the inflow of the US technology. As a result of its balance of payment surpluses, China has accumulated huge foreign currency reserves estimated to be over $2 trillion. Some 60 percent of Chinas official reserves are held in dollar-denominated assets. These trade and economic linkages dictate a cooperative relationship between the two countries. But there are also elements of competition between them in the economic field. Chinas growing appetite for fossil energy resources in Africa, the Persian Gulf region, Latin America and elsewhere, which pits it against the demand by the US for the same resources, is just one example of this competition. Chinas trade surpluses with the US year after year generate increasing US charges of dumping against China and demands for the appreciation of its currency and the opening up of its market. Environment is another area where the two countries are pitted against each other in terms of emission reduction targets for climate warming gases. But it is the strategic and political aspect of the relationship between the US and China, which will play a predominant role in determining its future direction. The US views Chinas rapid growth as posing a serious threat to its global supremacy and to its security interests, especially in Asia. Predictably, it is now engaged in a strategic manoeuvre of far-reaching consequences to contain China through an architecture of security alliances on the latters periphery. That is why the US has pledged to make India a major world player in the 21st century, why it entered into an agreement with India in 2005 for close military cooperation and why it has agreed to commence cooperation in civilian nuclear technology with India despite the crushing blow delivered by it to the international nuclear non-proliferation regime through its nuclear explosions of 1998. The US would also try to strengthen its security relations with other countries like Japan, South Korea, Australia, New Zealand and even the ASEAN countries for the same purpose. The US focus on China also limits the extent to which it can put pressure on Russia for achieving its strategic goals in Europe, Caucasus and Central Asia. The recent decision by President Obama to abandon the missile defence project in Poland and the Czech Republic is a reflection of this limitation. China has naturally reacted to the US initiatives by its own moves to protect its vital national interests. Its strategic partnership with Russia aims at countering the US global hegemony and unilateralism. The Shanghai Cooperation Organisation including China, Russia and Central Asia Republics excepting Turkmenistan as members serves the same purpose besides enhancing regional cooperation to combat terrorism, extremism and separatist movements within the member states. Chinas strategic relationship with Pakistan balances in South Asia the effect of the growing US strategic partnership with India. China is also engaged in diplomatic moves to strengthen its relations with the ASEAN countries, Japan and South Korea with which it maintains extensive trade and economic relations. Historically, the rise of a new great power, which challenges the prevailing world order, has led to tensions and wars with the established great powers. This was especially the case when the existing great powers were not able to accommodate the emerging great power through necessary adjustments in the global political, security and economic architecture. The question whether the 21st century would be a century of peace or of war and conflict will be decided fundamentally by the ability or the failure of the US and the Western countries to accommodate Chinas rise, by adapting the existing world order dominated by the West to the strategic compulsions of Chinas phenomenal rise. The writer is a retired ambassador. Email: javid.husain@gmail.com