When Alfred Nobel invented dynamite, he thought he had ended war, because nobody would think of unleashing such destruction on human beings. Same when Hyram Maxim invented the modern machine gun. They were wrong. Weapons don't get built to remain unused.
The first half century of the nuclear age has been dominated by the MAD (mutually assured destruction) theory. Since we were really talking about a potential war between just two mature powers, it would be impossible for a bomb to drop without knowing where it came from. With the advent of submarine missile launchers, a decisive first strike would be impossible. Therefore, an attacker could expect to be wiped out in the second wave. Thus, nuclear war wasn't practical, and the weapons remained on the shelf.
It's necessary today to consider whether MAD still has meaning in a world where nuclear arms are about to become commonplace. An automatic retaliation becomes problematic when you can't be sure which enemy launched. And some of these potential enemy states have few population centers or industrial facitilies worthy of nuclear targeting. If you had to drop a nuke on Iran, Libya, or even Afghanistan, what would you aim at? What could you possibly hit that would compare in importance to New York, Washington or Paris? What if the bomb was sent by a stateless entity like al Qaida? The whole concept of symmetric retaliation no longer works. Suddenly, the threat of a nuclear bombing seems more palpable than at any time during the cold war era. Sorry kids, it's a much scarier world out there than it used to be.