Assuming it happens it should look something like this...
Side 1: United States, United Kingdom, France, Germany, Israel, Canada, Poland, Australia, Italy, Denmark, South Korea, Philippines, Japan (only if its neutrality is violated), Saudi Arabia, South Africa, United Arab Emirates, Kuwait, Turkey, Portugal, Georgia, Morocco, New Zealand, Taiwan, Qatar, Bahrain, Vietnam, Thailand, India, Norway, and Iceland
vs
Side 2: Russia, China, Iran, North Korea, Lebanon, Syria, Pakistan, Burma, Egypt, Kazakhstan, Uzbekistan, Estonia, Argentina, Latvia, Kyrgyzstan, Cuba, Afghanistan (according to Afghan President Hamid Karzai, Afghanistan would join Pakistan in war), Tajikistan, and Mongolia (I am assuming Mongolia would be forced to aid Russia and China in the war effort)
There would probably be less militarily significant countries involved on both sides. I find it difficult to determine what side other South American countries would choose, or if they would even get involved. As for who would win, It is impossible to tell due to Nuclear weapons being a huge variable.
As a Vietnamese I took offence when people think Vietnam will ally with China. Just because Vietnam and China are both communist countries, it does NOT mean they are allies. The Vietnamese hated the Chinese because for a thousand years the Chinese targeted Vietnam for more land from many dynasties, they do not want the Chinese to take over their land, the 1979 Sino-Vietnam War, and the conflict of the dispute islands of Paracel and Spratly.
Japan is one of America's closest allies, so I don't think their 'neutrality' would have to be violated for it to join America. As for south america, I believe it would depend on which side Brazil joined, and, if forced to pick a side, I believe that Brazil would join America.
As for the war itself, it would likely be fought in 5-6 theaters of conflict. Theater 1 would be the Latin American theater, with Cuba, Argentina, and Venezuela (which I believe would join side 2) against the US and its Latin American allies. Theater 2 would be the European Theater, with the EU fighting against a Russian invasion. Theater 3 would be the Middle Eastern Theater, with Israel, Turkey, Saudi Arabia, the UAE, and the Caucasus coutries fighting against Iran, Syria, Egypt, and possibly Russia. Theater 4 would be the Indian Theater, with India fighting Chinese and Pakistani invasions. Theater 5 would be the Pacific/East Asian Theater, With South Korea, Japan, Taiwan, the Philippines, Thailand, Australia, Vietnam, New Zealand, and whatever American forces are stationed over there against China, and North Korea.
Theater 6 would be the Bering Theater, with either Russia invading Alaska across the Bering Strait, or the US and Canada invading Siberia, possibliy both.
I did not know there was a world war 3 World War 3 has not happend uless they diside to call the war we're in now WW3.
Yes, World war 3 is a really scary nuclear war.
I think you are slightly mistaken There is no world war 3.... :(
Russia suffered the greatest loss of life during World War I. There were thousands of casualties on all sides suffered during the war.
There is no World War 3.
Yes, because the two sides were very evenly matched for much of World War 1.
In the world war II Romania was allied with Germany
In the world war II Romania was allied with Germany.
Which gulf war? There were 3 of them.
both sides were locked in a stalement
Italy
Allies and Axis.
no they did not o.k
There hasn't been a world war 3 yet.
Italy was the only country to switch sides at the very beginning. Bulgaria and Russia switched sides late into the war.
there was no WWIII (world war 3)
Huh?? There has never been a world war 3.