The meaning, nature, and purpose of treaties changed significantly over two centuries, reflecting the greater complexity of international relations. Several developments contributed to this phenomenon. Among the more obvious changes that occurred in the second half of the twentieth century were the unprecedented rise in the world's population, the emergence of ethnic awareness around the world, an increase in the number of independent states, and developments associated with inventions in weapons systems, communications, and science, especially biochemistry. Treaties came to address not only the needs met by the relatively simple military security alliances and trade arrangements of the eighteenth and nineteenth centuries; they became also instruments for organizing and structuring the tremendously complex demands of an interdependent global geopolitical economic system. Treaties now dictated the conduct of nations in matters of global importance such as human rights, resource use and allocation, pollution, protection of the environment and animal species, intellectual property rights, and a whole host of hitherto unthought-of areas of national behavior. Despite the objections of individual nations, these international arrangements were proving remarkably successful in shaping international and domestic performance, and whether they liked it or not, most nations were linked into a complex international treaty system.
In this interdependent, international environment, the United States found itself in an anomalous position. It could no longer continue to enter—or refuse to enter—into treaty arrangements based solely upon domestic political considerations or an entirely independent assessment of whether or not unilateral action is preferable to multilateral action. The United States, although by some measures the world's most powerful military and economic power and free of the crippling shackles of the Cold War, could not ignore the responsibilities and restraints imposed by such institutions as the United Nations, the World Bank, or the International Monetary Fund, acting through a global, multilateral, treaty system. Nor could it ignore world opinion while seeking to take advantage of its membership in that treaty system.
Treaties came to impinge upon almost all aspects of the lives of Americans as well as the lives of most of the world's population. Perhaps the most dramatic change in respect to treaties was that they came to reflect the interests of global institutions as much as individual nations or their populations. This was as true of the United States as it was of other nations. A little over two centuries later, the worst fears of the Founders appeared to have been realized: the United States was involved in a series of world entanglements they could not have imagined.
Despite these views, it was not clear at the turn of the twenty-first century that the United States would accept the new order. President George W. Bush and his administration appeared to want to return to the nonentanglement envisioned in the days of the early Republic, and in their desire to do so they struck a resonant chord in the American people.