In 1939 the Soviet Union seized the eastern half of Poland. In 1940 it followed that up by annexing Lithuania, Latvia, Estonia, and part of Romania. In addition it launched a war of aggression against Finland, seizing about 10% of Finland’s total land area. Inhabitants in conquered territories were treated brutally. For example in the east half of Poland 10% of the population was lost due to deportation or outright liquidation.
FDR did not meaningfully pressure the Soviets to renounce their strategy of territorial aggression. Moreover, he did not put serious pressure on Japan to abandon its policy of expansion in China–at least not in 1937 when the wave of expansion in question had been released. FDR’s hard line stance against Japanese expansion did not manifest itself until 1941.
FDR’s warlike opposition to Japanese aggression in China was not the result of a universalist policy of opposing aggressive territorial expansion in general. If it had been, he would have been equally assertive in opposing Soviet expansion. Nor was his opposition driven by a particularist concern for the Chinese: he waited four years between the start of the Japanese offensive in China before initiating his efforts to provoke war with Japan. Those efforts started in 1941, shortly after Germany had invaded the Soviet Union.
Prior to Barbarossa, German military planners had anticipated having to deal with 200 Soviet divisions. By the mid to late fall of '41 they had already encountered nearly double that number. During the winter of '41 - '42, the Soviets shipped an additional 100 divisions west across the Trans-Siberian railway. Prior to Pearl Harbor, Stalin had held those divisions in reserve on his eastern front, to defend against possible Japanese aggression. With Japan going to war against the United States, Stalin knew that Japan would be too preoccupied elsewhere to launch much of an attack against the U.S.S.R. The hundred divisions in question could therefore be used on the German front.
None of the above could have been accomplished, had the U.S. and Japan signed a mutually acceptable peace agreement. That is why FDR’s administration ignored Japan’s various peace proposals, while pursuing a policy of deliberately provoking Japan into doing what it ultimately did.