It's not about any one nation ruling the world

In the end it's about equality. It's about raising enough food and distributing it well enough to feed all or most people. It's about having shelter and clothes and safety so enough people can survive without reverting back to being animals or something like that.

The main problems we are dealing with here on earth are actually overpopulation and lack of enough food being grown and the distribution of whatever is grown. Overpopulation is the single biggest problem the human race is dealing with where there is not enough fresh water to take care of the needs of those already alive. And because of global Climate change this likely will get much worse this century as glaciers and snow melts worldwide which will create times worldwide where there is no snow or glacier melt and therefore no water or not enough potable water available worldwide for people to survive.

The poorest people around the world will be the most vulnerable to extreme weather events like droughts, end of glaciers and snow, or polluted water because of poor sanitation in any given area on earth.

So, the challenge for mankind this century will be actually keeping the 50% poorest people alive worldwide and it might be important to recognize wherever there are wars this isn't going to happen because groups bringing food will not be able to feed people in war zones worldwide.

Another important factor is that without birth control in certain areas of earth it is inevitable there will eventually be wars and refugees there just like in the Middle East now.

So, overpopulation caused by no or not enough birth control would create wars anywhere on earth.

For example, China right now would be one of the most violent places on earth without birth control like they have had since around the 1970s. Instead, things are relatively okay for 1.4 billion people in China compared to what a mess it could be without birth control.

However, since there are many more men now than women because of this it is also causing many social problems as well. But, if you compare China to the middle East in this you can better see what a complete disaster the middle east is without enough birth control and how likely it will stay a mess the rest of this century or longer because there is still not enough birth control there to create any kind of balance in a desertified area without enough potable water or areas to grow food.

So, this century will not ever be about really big wars like world war II because that would be the end of the world and all life upon it and everyone realizes this.

However, it will be about: "How do we deal with overpopulation various places on earth?"
And "How do we get enough potable water so people don't all die of waterborn diseases?"
And "How do people survive extreme winds and extreme heat and extreme precipitation in some areas around the world" and conversely, "How do poor people survive extreme droughts when the only way they can survive is to grow their own food?"

These are some of the real problems that will exist the rest of this century and beyond.