Giuseppe Garibaldi, who united Italy in the 1860s, was asked by Lincoln to run the army during the US Civil War. Garibaldi said he would if Lincoln officially declared that the aim of the war was to end slavery. Lincoln replied that he couldn’t at that time, and so Garibaldi moved on to other things.
While researching this entry, I’ve seen how much things could have changed had Garibaldi gotten involved in the war. There’s an anti-catholic page about him, the white supremacists seem to like him (why, if he was so anti-slavery?), the French hated him, the English loved him. Had he led the Federal troops, would France have jumped in on the side of the South? Would England have then jumped in on the Union side to counter? The Papacy would clearly have denounced the North (indeed, the pope was the only world leader to recognize the Confederacy). A whole different world history, perhaps, hanging on a yes/no question.