From J-Wiki

American + Asian, usually connotes the children of U.S. servicemen and Asian women. Perhaps first used by Pearl S. Buck, in her novel East Wind, West Wind [published in 1930]).

An Amerasian is an individual of American and Asian, especially East Asian ancestry. Historically, the term referred to children born to local women and American servicemen stationed in East Asia during the Korean and Vietnam Wars. It should not be confused with Asian American, which describes an American citizen of full or partial Asian ancestry. It's estimated that by 1952, anywhere from 5,000 to 10,000 Japanese children were fathered by American servicemen, with many of the children placed for adoption by their Japanese mothers due to the stigma of out-of-wedlock pregnancy and miscegenation and the struggles of supporting a child alone in post-war Japan.