I'm assuming you mean World War II. Both the U.S. and the Soviets felt a distinct need to rebuild in the wake of the war. However, the United States did not need to "rebuild" itself. America was not directly struck - save for the attack on Pearl Harbor - during the war. Russia, however, was decimated in the attack. Russia, also, was poverty ridden after the war and had suffered from the loss of several millions of soldiers killed in the war. The Russians were left deeply suspicious and fearful of being invaded by other powers, hence their rebuilding focused on arming themselves in order to prevent another invasion. The U.S. was in a strong financial position after the war and used its resources to arm itself - in response, in part, to the Russian's militarization - and invest in rebuilding Western European allies.
