Tensions between the US, Russia, China and North Korea have continued to escalate in recent times
Donald Trump launched supersonic B-1B bombers from Guam airbase and warned “America WILL be defended” as North Korea threatened to attack the US naval outpost.
Prior to that, North Korea conducted two nuclear tests and 24 ballistic missile tests in 2016 alone, defying six UN Security Council resolutions banning any testing.
- How else could World War 3 start?
Russia and America's involvement in the war in Syria has created a situation where the two nations' planes are reportedly flying dangerously close to each other on bombing runs.
Putin threatened in June to shoot down all RAF and US jets in western Syria in retaliation for a US Navy fighter downing a Syrian plane.
If World War Three does kick off it seems the Russians could have something to do with it.
But it is more likely that if it ever did happen, it would be sparked hundreds of miles away from Syria.
- Who would win the war?
It is impossible to say who would win with any certainty, but the US spends far more on its military than any other nation.
The US is the only country in possession of fifth-gen fighter jets - 187 F-22s and an F-35 that is not yet out of the testing phase.
Russia is developing one stealth fighter and China is working on four.
In terms of submarines the US Navy has 14 ballistic missile submarines with a combined 280 nuclear missiles.
They also possess four guided missile submarines with 154 Tomahawk cruise missiles each and 54 nuclear attack submarines.
Russia has only 60 submarines but they are said to have outstanding stealth capabilities.
They are also developing a 100-megaton nuclear torpedo.
China has five nuclear attack submarines, 53 diesel attack submarines, and four nuclear ballistic missile submarines to date.
But the emerging superpower is developing more.