Look up Lost Cause of the Confederacy. Perhaps the biggest celebration of the losing side in history. Or the first Rocky movie.

> Americans only support the underdog when the underdog wins in the end.

By that definition the by far most cited example on the British side, Dunkirk, doesn’t count because Britain won in the end.

No one celebrates someone who was defeated if the defeat wasn’t memorable. Usually that was because it was an inspiration to rally a cause that was later successful.

Plenty of white people celebrate Custer. Search for “Custer statue” or drive around out west and see how many paintings of Custer’s last stand you can spot hanging in bars.