There won't be another "world war" if you think that means fighting with guns, tanks, and fighter jets. 21st century war is being fought under our noses as "unrestricted warfare" (https://www.c4i.org/unrestricted.pdf). Information warfare, legal warfare, economic warfare, etc. are how battles are fought. Why would a country want to shoot bullets at the US when they can control or dismantle it from within?