The spanish civil war was 36-39 and the second world war is generally understood to start in 39 with Hitler's invasion, so although they share a very significant context, the civil war is not the second world war.
Furthermore, the events leading up to Spanish Civil War were internal and completely unrelated to the looming global conflict, regardless of the fact that the Axis powers and the USSR chose to support different sides for ideological or opportunistic reasons.
All else being equal, the Spanish Civil War would have happened even if Italy, Germany and the USSR hadn't intervened in any way whatsoever (though what the result would have been is anyone's guess), and WWII would have happened all the same even if the Spanish Civil War had never happened or if the Spanish Republic had managed to prevail.
