That is a ludicrous comparison that, by the way, is based on Soviet and Chinese Communist propaganda. You have no clue what you are talking about regarding Japan's actions in China.
You do realize that Japan was capitalist and anti-Communist, right? You do realize that Japan was the most Westernized nation in Asia at the time, right? You do realize that Japan's main opponent in Manchuria was not the Chinese but the Soviets, right? You do realize that Japan acquired Korea after defeating Russia, which was trying to acquire Korea too, right? You do realize that millions of Chinese sided with the Japanese against the Nationalists and the Communists, because they brought stability, law and order, and economic progress, right?
Leaving aside the questionable claim that Japan started the war in China, I take it you want to condemn the lesser of the evils in Asia. The Japanese army did not kill nearly as many innocent people as did the Soviets and the Chinese Communists, and they arguably did not kill as many people as did the Nationalists. In some places, such as Korea and Taiwan, Japanese rule, by any rational comparison, was moderate and beneficial.
Truman handed China over to the Communists and sentenced tens of millions of Chinese to death in so doing. Because of FDR's and Truman's pro-Soviet/pro-Communist policies on China and Korea, China fell to the Communists; the Soviets gained valuable territory in Manchuria and on key coastal islands; and we had to wage a bloody war in Korea just to free half of the country from the Communists, something that would not have been necessary if we had not demanded that Japan abandon Korea.