World War 1 was really a European adventure, with the US getting involved. But most of the world sat that one out. World War 2 at least had a representative from another continent, making it mainly European, but with participants in North America and Japan. South America, Australia, most of Asia, the Indian subcontinent, et cetera, sat that one out.

So it seems like the concept of a "World War" doesn't really need to involve the whole world, or even most of it.

Both world wars weren't a waste of life, unlike the one that should've ended a couple years ago(AKA, the one we are in right now). Besides, we went into Iraq to search up some WOMD(weapons of mass mcblah blah...) , seize Saddam Hussein, establish democracy. Did all those, but let's send 21000 more people for the heck of it.