Question

Proxy wars were primarily a product of

Answer 1

Proxy wars were primarily a product of

American attempts to gain colonies
the Soviet policy of the domino theory
Soviet attempts to engage in a war with the U.S.
the American policy of containment

Answer 2

http://en.wikipedia.org/wiki/Proxy_war

Answer 3

The domino theory was not a Soviet policy. America's brief attempt at imperialism was in the years around the 1900s, proxies were not used. The Soviets and Americans avoided direct conflict during the Cold War (actually, World War III. But nobody calls it that)
So that leaves containment. That's only partly true, because the Soviets used proxies too.
But D is your best answer.