Oh, heck, Elmore, anyone will unite with anyone to defeat what they see as a common political enemy. Countries do it all the time. Why wouldn't competing religions do it too? Differences are forgotten until the greater common enemy is out of the way!

Example: USA, Great Britain, and Soviet Russia work together happily to defeat Nazi Germany from 1941-45. Almost the moment Germany is kaput, the western Allies and the Russians become sworn enemies again...toot sweet...and the next great conflict begins.

It's standard human behaviour. Pragmatism almost always trumps principle...specially in politics and business.