If you want to get metaphysical about it, the terms war and peace only make sense if both exist. The history of humanity may be full of war, yes, but it wasn't some sort of warhammer 40k dystopia constantly either. By definition the idea of war can only exist if there are periods of peace, and vice versa. War is the absence of peace, peace the absence of war.
Maybe if some group of people are unethical enough to literally change human nature (something that's starting to become more possible over time with breakthroughs in genetic manipulation) you could maybe have "eternal" peace. I'd argue humans aren't what they would be defined as at this point.