In Battlefield 4, US is the main protagonist country while China is the main antagonist that they went to war in 2020.
Throughout the campaign, NATO forces (US & Europe) are fighting against Russia & China in the story is considered World War 3?
Well, I would call it "local" conflict. Despite three major countries are involved (RF, China and USA) most of the combat operations happened on Chinese soil/water. After all, it was rogue Chinese general, who took over the country (briefly) and tried to start the real WW3.