"Some analysts^[1] and historians^[2] have suggested that the Cold War can be identified as World War III because it was fought although by proxy on a global scale, with the main combatants, the United States and later NATO, and the Soviet Union and Warsaw Pact countries providing political, military and economic support while not engaging in direct combat.^[3] In a 2006 interview, US President George W. Bush labeled the ongoing War on Terror as "World War III" also.^[4]"

Assuming we've already had or are already in WW3 when will be world war 4 and what could cause it ?

My guess is that it will erupt during a particularly rousing debate over when and where WW3 actually occurred...

"I don't know how man will fight World War III, but I do know how they will fight World War IV; with sticks and stones."

-- Albert Einstein

If ever, it would definitaly begin in Eastern Europe, probably between Russia and Ukraine or baltic area countries. Since these countries are for the most part NATO affilates or are becoming such, the entire organization would have to come into the conflict.

Reason for the war? Russia and its never ending dream of being a international powerhouse which has to be respected and given what it needs.

I wouldn't call the Cold War WW3...and since most people don't, it pretty much is that way.

Nuclear bomb set off by terrorists and retaliatory offensive taken on the wrong nation. That would do it.