Italian statesman, military genius and world-trotting General Giuseppe Garibaldi was offered a generalship in the Union Army, but the US declined to meet his conditions for employment. He had two demands, as outlined by an American diplomat in contact with him:
He [Garibaldi] said that the only way in which he could render service, as he ardently desired to do, to the cause of the United States, was as Commander-in-chief of its forces, that he would only go as such, and with the additional contingent power–to be governed by events–of declaring the abolition of slavery; that he would be of little use without the first, and without the second it would appear like a civil war in which the world at large could have little interest or sympathy.
Many men who fought with Garibaldi did take part in the American Civil War, however, on both sides.
Confederate Identity Project 