Yea well they should have stuck to the simple rule of "Don't piss off the British Empire."

But think about, Germany had left the western world alone and Britain still had its Empire.

Germany wanted Britain as it's ally during the War, but they went and forced us to step in to honour a treaty. They called our bluff and got an ass kicking. Also Britain would never allow Europe to be conquered, it's been the rule of thumb for the survival of Britain that it can never happen. A united Europe is a massive threat to us hence the massive reluctance for a political union on both a national and European level.

Unfortunately Poland was the only country lying between Germany and Russia, it's very possible Germany would have straight gone to war against Russia while leaving everyone else alone if they had their back secured.