Question

the arms race meant that once the united states built hydrogen bombs, the soviet union built them too. world peace had been assured. no other country wanted to build them. a new world war was about to start.

Explanation:

The arms - race during the Cold War was a competition between the US and the Soviet Union. When one side developed a new and powerful weapon like hydrogen bombs, the other side would follow to maintain a balance of power. World peace was not assured, other countries did have interest in such weapons in some cases, and while tensions were high, it didn't mean a new world war was immediately about to start.

Answer:

the Soviet Union built them too.