because, like America, England, and some other countries, China did not like what Germany was doing. they were forcing christianity on people, on jewish men and women, and they didnt like that so they rebeled, and when that happened, they started bombing places making camps to "enslave" in a way, the Jews because they did not accept there religion. in a way, they were the bullies, and America, China, England, and France, did not like that, so they declared war to protect the innocents.