Soong was in charge of negotiating with the Soviet leader Joseph Stalin regarding Soviet interests in China, and traveled to Moscow to extract from Stalin a guarantee to oppose the Chinese Communist Party. Soong conceded to Stalin the Manchurian railways and Korean independence, but refused to allow Russian interference in Xinjiang or Russian military bases in Manchuria; he also indicated that China and the Soviet Union could share dominion over Mongolia if a "mutual assistance pact" was agreed to. Soong was known for his tough negotiating style with Stalin, getting straight to the point and freely using the threat of American military backing to strengthen his demands. When the Sino-Soviet treaty was signed, China ceded to Russia parts of Mongolia, use of a naval base at Port Arthur (with civilian rule remaining Chinese), and co-ownership of the Chinese Eastern Railway in Manchuria. In return, Soong extracted from Stalin recognition of the Republic of China as the legitimate regime of China, aid from the Soviets, and oral agreement to an eventual Soviet withdrawal from Manchuria. The treaty failed to end tension in China with the communists, resulting in renewed fighting in the Chinese Civil War. Stalin had previously told the Americans that President Roosevelt should inform Chiang Kai-shek of the Russian demands in Manchuria, at the Yalta Conference, before Stalin informed Soong.