They had a loose alliance from 1936 and signed the tripartite in 1940 but that really amounted to keeping out of each other way and sharing information. They only mutually declared war on the US a week after Japan bombed pearl harbour. The US was still profiting from both sides of the European theatre up until then so whos to say what backroom negotiations were happening between Germany and the US in that week. The Nazis werent really renown for treating people from different ethnic groups as equals so who's to say what their first preference of allies were. We can only rely on our written history which is conveniently written by the winners ..