When the Cold War ended in 1991, so did World War II. For the United States, this was one very expensive conflict. It ended up costing the United States some twenty trillion dollars (in current dollars), 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, 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.