Trump gonna get his card pulled a lot
Sometimes you have to go to war, because others make it impossible not to do so. Russia and China have been stepping past the line for years.(I know, I've worked for the military) Putin is a dude that wouldn't mind trying to take over the world, and he has China as something of an ally. Eventually (and I mean probably soon) it's going down. The fight over control of natural resources is a big part...
But all of it is a means to an end. The United States has been falling back to the pack. Even though it's still big, power has been shifting back over to Europe for a while now. The European Union, which is pretty much the United States of Europe, has a larger economy combined than the U.S. right now. The U.S. still spends more money on military defense than any other country, but that's because it's pretty much the U.S., Israel, and a few other allies against the world at this point.
World War 3 is going to happen, and it will be worse than both World War 1 & 2 combined because of the invention and development of nuclear weapons. The end of World War 2 was just a glimpse at what's going to happen in the next World War. All it takes is one greedy, self-obsessed, power hungry individual to cross a line and then 1/3 of the United States and the World is destroyed by atomic weaponry. Because once that first rocket gets launched and everybody realizes what it is, then more will follow. The Chernobyl nuclear disaster took place over 30 years ago, and they just completed a 100 year protective shelter over the site because of it being so destroyed by nuclear material, making it uninhabitable. That's the power and destruction of nuclear material. Nuclear weapons kill on contact (explosion,fire) and over time (radiation poisoning, cancer).
In the end, it's all about whether you're ready to go or not, because it can happen at any time at this point.