The 1950s:

Although the friendly Soviets are no threat to the United States, the U.S. government seeks to ensure its new superpower status by building a better bomb. During the late 1940s, work progresses rapidly on a more powerful cousin to the atomic bomb -- the hydrogen bomb. In August 1950, the first H-bomb is detonated in the South Pacific, obliterating a small island. During the next decade, the United States demonstrates the power of these super bombs by setting off more than 50 of them on land, in the air and underground.

The rest of the world responds slowly. Several European countries and the Soviet Union build small nuclear arsenals. Taking caution to appear friendly toward the United States, they allow it to set up military bases in their backyards to deliver its bombs when necessary.

There is no space frontier for the United States.