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 between the U.S. and Soviet Union was characterized by mutual escalation. When one developed a new weapon, the other followed to maintain parity. The other options are incorrect: an arms race did not assure peace, other nations later pursued nuclear weapons, and a direct world war did not start immediately after H-bombs were built.

Answer:

the Soviet Union built them too.