People in 1900 thought humans would all kill each other too

 Then millions died in World war I from especially England, Germany and France that died by the millions mostly in the trenches. Then Americans entered world War I late like we did in World War II only because we wouldn't sell Japan any oil and the Samurai honor code forced them to attack Pearl Harbor. Then around 100 million people died and 20 million died just in Russia when Germany attacked Russia during the winter. This broke the back of the German Army sort of like Napoleon attacking Russia in the 1800s. It gets really cold in Russia in the winter and if you don't have somewhere to get warm and food to eat you are going to die like Russians and Germans did in Russia. Same with Napoleon in the early 1800s.

So now, we have Trump who won't defend Ukraine against Putin which will start a series of Dominoes where Ukraine is gone then Poland is gone then all the rest are gone.

Why are we doing World war I and World war II again with Russia playing the part of Germany?

That's Crazy!

When people ignore History they are doomed to repeat it.