You have to have enough imagination to briefly put yourself inside the mind of the average young German soldier at the time, Pete, and understand what he was thinking about. I gather you haven't ever tried to do that?

# 1 - They were under the false impression that the war started because Poland had committed vile atrocities on ethnic Germans in Poland (rape, robbery, violence, etc) and had sent a raid across the German border. This was what their government told them. It was all lies, but they didn't know that. They believed what they were told, just like most people everywhere do when their government tells them the nation is being threatened.

# 2 - The Germans didn't declare war on Britain and France over Poland. The British and French declared war on them. Again, they were under the impression (this time a correct one) following that that they needed to defend their country against the British and French...2 major powers, both considered in the same league as Germany when it came to fighting a war. Defending their country was the first thing in their minds from that moment on, and once the fighting starts: YOU FOLLOW the orders YOU are given. This is true in EVERY armed forces of every nation. And you go where you are told to go. And you figure it's necessary to defend your side.

# 3 - They had been taught for a generation that Germany had been oppressed and betrayed by the Treaty of Versailles (and that was true) and that the country was threatened from within by Jews and Communists (that was untrue). They believed all of that too.

They honestly believed they were defending Germany. That led to military campaigns which rapidly took them across borders into many other countries. Everyone crosses borders when the fighting starts...IF they possess the expertise to win the battles that are waged on those borders. And you don't stop till you've won or lost the campaign, beaten the enemy or been beaten by them. If you're winning you invade.

Present day American troops are told that they are defending the American way of life and defending "freedom" by invading distant foreign places like Iraq and Afghanistan. That too is a blatant lie. They are not defending the USA, they are helping to bankrupt it. But a lot of them believe the lie that they are defending their nation. You CAN be the aggressor, you can invade and occupy other places, and you can still be quite convinced that you are legitimately defending your homeland. It's happening right now in the Middle East and western Asia, and Americans and their western Allies are doing it. They ARE the German Blitzkrieg of the present era...very good at their job, which is killing people and securing vital strategic resources and political puppets for big American corporations.