How did the u. s and the soviet union start the arms race?

Not long after World War II ended in 1945, new hostilities emerged between the United States and the Soviet Union. Initially, only the United States possessed atomic weapons, but in 1949 the Soviet Union exploded an atomic bomb and the arms race began. Both countries continued building more and bigger bombs.

Explanation:

Secretary of state, staunhly anti-communist, proposed that the United States could prevent the spread of communism by promising to use all of its force, including nuclear weapons, against any aggressor nation.

--Magnus