Travel between universes is banned to, unless its the FTL thing where you drop into one to get to another part of your own faster, but its not allowed to go and claim resources from them.
And it is possible to be as powerful as the BIg Three, but just not more powerful. They represent the limit on how powerful a nation can become.

As for my grammar I am working on it, but a few of that tends to be writing quirks. I really dislike the English language because it has a lot of unnecessary grammar rules, so I tend to develop my own way of doing things.