High probability that WW III would not be fought by every country exempting most South American, African, and Oceanian countries and a good number of Asian countries. So many countries were involved in WW II just because colonial powers ruled them.
Team West
USA
UK
EU
Canada
Japan
Taiwan
Israel
South Korea
Saudi Arabia.
Team East
Russia
China
North Korea
Iran.
If WWIII initiate in south china sea, battlefield will be Asia, otherwise it will be europe.