It's a fundamental attribute of reality. Take it up with mother nature, because power struggles exist everywhere, even in dumb systems with no intelligence. Weak things go away, strong things stay around. Weak things need to become stronger than strong things to displace them.
Not really, kindness also exists. It is the escape hatch from the evolutionary zero sum game and let's you pick a better equilibrium (bargaining vs pure Nash).
We can just not fight. There is enough room and resources,we can get more of them and build more efficient tech, and we are all more alike than different.
There's more than enough energy and resources to go around for humans to peacefully coexist "forever", albeit in lesser numbers than today. The civilization meta game is what ruins it, despite our best attempts to regulate that. And a global self destruct button helps massively... until it does not.