Try it and see for yourselves. Of course, it's easier to believe what you see, because God is a spirit and can't be seen, but the good results of applying what Jesus said shows God exists and he is good. It's easier to do by our human nature: if you don't have something, to take it from somebody else, but you wouldn't like it if somebody took something of yours. This same way as you said Germany had tried to do, and you see the results - it was defeated, so revenge does no good. So Jesus was right about turning the other cheek, instead of hitting back.