The basis is the context, is globalization. In prehistoric times a tribe where the people you'd physically meet. In a globalized world the tribe is much bigger, because of communication, commerce and transportation technologies broke the limitations of physical connections.
> Is it a falsifiable scientific fact?
No, it isn't. But it is something that mostly works. Life just feels better when you treat others the way you want to be treated by them, when you and them share the same rights. You see, Karl Popper (the "falsiable" guy) wasn't 100% correct. We actually have a lot of stuff in science that is just a convention and isn't "falsiable". E.g. how cold you possible demonstrate to be false the basic geometric elements: a point, a line, a plane. They don't really exist physically, they're just abstractions.
The general rule is that, in general, cooperation is better than war. War is too destructive and is even more destructive when it targets a complex society (because there is more to destroy). With cooperation, in general, you avoid the destruction of war.