Final answer:
The Soviets were promised holdings in Asia during the Yalta Conference to gain their support in the Pacific War against Japan, secure their participation in the United Nations, and to ensure Soviet influence in Eastern Europe postwar.
Step-by-step explanation:
During the Yalta Conference, the Soviets were promised holdings in Asia as a strategic move by the Allies. The primary reasons were to secure Soviet support in the U.S. Pacific War against Japan, to ensure Soviet participation in the newly proposed United Nations, and to maintain a balance of power postwar. Stalin agreed to declare war on Japan three months after Germany's surrender in exchange for territorial concessions and influence in Eastern Europe. Free elections in Poland and other promises made by Stalin were met with skepticism by Churchill and Roosevelt, who suspected that Stalin would install pro-Soviet governments. Nonetheless, the agreement included U.S. recognition of Mongolian independence from China, Soviet interests in the Manchurian railways, and Port Arthur. These agreements were made without Chinese representation or consent.