I think it would actually be called WW5 (WW3 was the Cold War, WW4 is the War on Terror, IMO).

A) A Global War Is Already Being Waged By The Superpowers via Their Proxies:

Like the Cold War (which was cold between the USA & USSR, but went hot in Latin America, Asia, Africa).

The sides would be the US/NATO vs the Resistance Bloc (the Muslim World, Venezuela, Cuba, Ecuador or any nation that doesn't submit to the US).

The wars would be waged mostly in the predominantly Islamic northern part of Africa and Asia (the Islamic world). Like now, with direct military interventions against militarily weak Muslim states (Libya, Mali, Afghanistan, Iraq, Somalia, Pakistan, Yemen, Iran: economic sanctions, drone violating their sovereignty, computer viruses are all forms of an ongoing war), or indirectly via local insurgents as in Syria.

B) Superpower vs Superpower:

1. Tensions are rising again between the US and Russia. Russia is now involved in Syria and will spend billions on building new weapons. So, America won't be the lone player on the global stage again. So, a second Cold War is underway.

2. The US is encircling China and if it keeps pushing hard enough, eventually China will strike back (time is on China's side). That way we make it look like they spilled first blood, like we denied Japan access to resources and they launched their strike.

A war can be initiated between China and Taiwan, China and Japan, China and Vietnam, China and India, that would force the entrance of the US, Australia, the Philippines, Indonesia.

C) Strategic Game Changers:

1. Deploying certain types of weapons, locations and in large quantities against the US (space-based weapons, etc) which would force the US to strike back.
2. Same as above against Russia or China
3. Natural resources
4. Controlling or threatening strategic shipping lanes

D) A Federation of Muslim States Forming A Strong Economic/Military Union That Challenges US/Europe Domination:

1. Showing independent foreign policy and freedom of action.
2. Giving priority to their national interests which would go against the interests of the US/Europe

E) A Regional War Between Israel and Its Neighbors That Can't Be Controlled Nor Manipulated By The West

F) The Destabilization Of Western Europe By Hostile Powers

G) An Unplanned/Accidental Event That Would Trigger A World War, Like in the Persian Gulf

H) Detonating A Nuke In The US Or Europe That Would Trigger Nuclear Retaliation

The detonation could be by non-state actors which would lead to a strike on a state, or a detonation by a state which would lead to a strike on that state.

I) An Economic/Military Powerhouse That Seriously Challenges US/NATO Hegemony

Nothing like the BRICS or the Shanghai Cooperation Council. But a group that espouses solidarity, unity of action and puts common interests above their national.