Last month, the United States withdrew from a landmark missile treaty with Russia. Another crucial arms control treaty, the New START agreement, is set to expire in early 2021. China and several other countries with nuclear weapons, unconstrained by any treaty commitments, have been building up their arsenals. But as the global arms control architecture has frayed and weapons stockpiles grow, one pillar holds steady: only a handful of countries worldwide have nuclear weapons, and the risk of new entrants into the club, most experts agree, is relatively low.
On balance, the United States’ nonproliferation efforts have been remarkably successful. No country that does not already have nuclear weapons seems to be developing them, although some, such as Iran, have the capabilities to do so. Most countries have opted not to build their own warheads in part because international treaties have erected legal, political, and normative barriers to the bomb and in part because the United States has made extensive security commitments to its allies around the world. Washington and its partners have also established that those who get caught proliferating face tough penalties.
But although nuclear proliferation has remained mostly in check so far, there is reason to doubt whether it will do so indefinitely. The international order and the United States’ role within it are changing. The treaties, security commitments, and sources of leverage on which nonproliferation rests may not survive these shifts. Washington shouldn’t be surprised if the nuclear landscape—and its ability to manage it—soon changes for the worse.
THE WRITING ON THE WALL
Today’s consensus on preventing the spread of nuclear weapons did not always exist. In the early years of the Cold War, some in the United States argued that proliferation was inevitable and that having more nuclear-armed states on Washington’s side could actually be an advantage. But the winds shifted by the mid-1960s, and Washington and Moscow both realized the risks of open-ended proliferation. By 1970, both sides backed the Treaty on the Non-Proliferation of Nuclear
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