Arrange the events of the arms race in the correct sequence.
The United States created three bombs as a result of the Manhattan Project.
The United States detonated the first thermonuclear or hydrogen bomb.
The Soviet Union detonated its first atomic bomb.
The Soviet Union’s spies gathered information about the US Manhattan project.

The correct order of events (with dates and notes following):

The Soviet Union’s spies gathered information about the US Manhattan projectThe United States created three bombs as a result of the Manhattan Project. The Soviet Union detonated its first atomic bomb.  The United States detonated the first thermonuclear or hydrogen bomb.

Details:

Soviet espionage concerning the Manhattan Project occurred all the way along the line during the project, from 1940-1945.The first bomb, called "Gadget," was detonated as a test model in July, 1945.  The "Little Boy" and "Fat Man" bombs were dropped on Hiroshima and Nagasaki in August, 1945.The Soviet Union tested its first atomic bomb in 1949.The US achieved development of a hydrogen bomb in 1952.