History plays cruel tricks. Take, for example, 1991 and the end of the Cold War. This was to make possible a golden age of peace and prosperity. If didn’t work out that way.
When the Cold War ended in 1991 so did, for most of the world, World War II. Most people thought the future would be different, in a good way. Defense spending declined through most of the 1990s and everyone, including most Americans, expected there to be less call for American armed forces overseas. Many foreign U.S. bases were closed and the only ones complaining were the thousands of foreign workers hired to help run these bases. This ended a century of overseas military activity, which began with the Spanish-American War in 1998 and was always unpopular with many Americans. This was because, as many American allies tend to forget, most Americans are descended from people fleeing war or disorder in their homelands. In short, Americans tend to be more anti-war and isolationist that most.
But after the horrors of World War II and the continued threat from Soviet Russia Americans were willing to put up with high defense spending and peacetime conscription (both foreign to the American experience). Despite growing anti-war sentiment, especially during and after Vietnam, the majority of Americans, many reluctantly, supported continued overseas commitments. But after 1991 the attitude was that America had done its job, the 90 year war (that began in the Balkans before World War I) was won and things would change.
Unfortunately things did not change. China decided it wanted its ancient empire back and Russia, after two decades of sorting out the wreckage of its Cold War defeat, decided that it was time to rebuild the old Russian Empire. At the same time Islamic terrorism, fueled by decades of high oil revenue, became a worldwide threat. Suddenly America was being called on to take the lead (and handle much of the expense) of dealing with these threats. Americans, in general, are not too pleased with this new demand.
The main reason for the American reluctance was that for the United States, the 90 year war that ended in 1991 was one very expensive conflict. It ended up costing the United States some twenty trillion dollars (adjusted for inflation), from 1940 to 1991. Surprisingly, some 30 percent of this spending went for nuclear weapons and the missiles and aircraft that delivered them. Indeed, we tend to forget that, as expensive as the World War II "Manhattan Project" (to develop the atomic bomb) was, the parallel project to develop the B-29 bomber (to carry the atomic bomb) actually cost more. As expensive as the nuclear weapons programs were, they were also a success for two reasons; they were never used again after 1945, and the possibility that they could be used persuaded the superpowers to not fight each other. This last item was real, as there has never, in modern history, been such a long period of peace between the major military powers on the planet. Moreover, the end of the Cold War did not reduce spending on nuclear weapons, at least not if you add in the costs of developing defenses against nuclear weapons. Missile defense, and homeland defense have replaced the billions spent annually on new missiles and nuclear warheads. While Russia has shifted most of their nuclear weapons spending (which was about 20 percent of their defense budget) to non-nuclear weapons. But despite the end of the Cold War, it looks like the United States is going to be spending 30 percent of the defense budget on "nuclear weapons" for some time to come.
The problem with still having all these nukes was that the threat from Russia, China and Islamic terrorism did not involve nukes. Oh, Russia may threaten to use them and Islamic terrorists may seek to buy or steal one, but the reality is that all the players here are willing and able to be a problem without confronting nukes head on. But the nuclear threat is still there and the United States is the largest and most capable nuclear power on the planet. American allies expect the yanks to be available to make it all better, or at least help avoid a nuclear holocaust. The problem is getting a majority of American voters to agree and keep them agreeing. It’s not just nuclear support American allies want, they now want American troops to come and set up shop in foreign areas that are threatened. This is a tough sell in post-1991 America where there is still a strong belief that the Cold War is really over and any lingering problems overseas can (and should be) be taken care of by the locals.