During World War II, the Republic of China was an ally of the United States, and the federal government praised the resistance of the Chinese against Japan in the Second Sino-Japanese War, in an attempt to reduce anti-Chinese sentiment. In 1943, the Magnuson Act was passed by Congress, repealing the Chinese Exclusion Act and reopening Chinese immigration. However, at the time, the United States was actively fighting against the Empire of Japan, which was a member of the Axis powers. Anti-Japanese racism, which spiked after the attack on Pearl Harbor, was tacitly encouraged by the government, which used slurs such as "Jap" in propaganda posters and even interned Japanese Americans, citing possible security threats. American soldiers who fought in the Pacific theater frequently dehumanized their enemies, leading them to mutilate Japanese war dead. The racist nature of this dehumanization is revealed by the different ways in which corpses were treated in the Pacific and European theaters. Apparently, some soldiers mailed Japanese skulls home as souvenirs, but none of them mailed German or Italian skulls home. This prejudice continued to exist for some time after the end of the war, and anti-Asian racism also affected U.S. policy during the Korean and Vietnam Wars, even though Asians fought on both sides during both of those wars as well as during World War II. Some historians have alleged that a climate of racism, with unofficial rules like the "mere gook rule", allowed a pattern to exist in which South Vietnamese civilians were treated as if they were less than human and war crimes were also common.