Why did France and Britain declare war on Germany after Poland?

Had the UK and France taken immediate action, Germany may have been in serious trouble. Their western front was not well defended and they were badly outnumbered. They were hoping France and the UK would not act at all - a reasonable hope given that they completely rolled over on the Czechoslovakia issue. Hope B was that they’d just act slowly, which is the hope that came through.

Good points.

France and Britain didn’t do anything about the Soviet invasion of Poland for the simple reason that there wasn’t anything they could do about it in the first place. Due to the geography of where Germany, Poland, and the Soviet Union were in relation to France and Britain, they had no way to reinforce or help Poland. It is the old rule of politics or command. Never issue an order or command that you know will not be followed, and you have no way of enforcing. All it will do is make you look stupid and more incompetent.

The 2nd big reason is simple realpolitik. The Allies were already at war with Germany at the time of the Soviet invasion. Adding another enemy that is so far away you have no real way of attacking would be incredibly stupid and would accomplish nothing but negative things for the Allies.

Then why declare on Germany?

It would show they werent being hypocritical.

The sad thing is that France did launch a local offensive during the Sitzkrieg (“Phoney War”) portion of WWII that was very successful. The Saar Offensive (7 September – 16 October 1939) took very low casualties. It captured 12 German towns and villages and advanced 8 kilometers into German territory. The French abandoned it and withdrew back to the Maginot Line after it was obvious that Poland was going to fall. They did this because they thought defense was stronger than offense.

Given how successful it was and how little of the German army was on the Western Front, it is extremely likely that if France had launched a general offensive instead of just a local one, the entire German front would have collapsed.

To be fair, there are reasons that France didn’t launch a general attack. Part of it was fighting using the last war’s tactics in the current war. Part of it was that the French felt like they did all the fighting and dying in the beginning of WWI while the US and British built up their militaries, and then the British and Americans took all the credit for winning the war after the French attacks had worn down the German army. They didn’t want to repeat that experience. Another part of it was they had spent billions of francs on the Maginot Line and really believed it would work.

Simple. They weren’t at war with the Soviet Union at the time. Also, they could attack and reach Germany, but they couldn’t attack and reach the Soviet Union. As others had noted, they already had a treaty with Poland to defend them from Germany but not to defend them from the Soviet Union.

Shrug, when the stakes are that everyone with the wrong kind of nose or last name in your country dies, and everyone else is turned into slaves for their empire, no one gives a shit if they are being hypocritical. (Hopefully that comes across as funny instead of rude.)

I would like to expand on your point a little bit if you don’t mind. I agree with your point and would add that Czechoslovakia changed both the Allies’ and Hitler’s thinking.

Hitler now thought that he finally had the French and British thinking figured out. All he has to do is push really, really hard for something Germany arguably had in the past and then threaten war, and Hitler would get it.

The French and British learned the opposite lesson. They learned that no matter what they gave Hitler, he was always going to ask for more later. There was no point in appeasing him, as it just made him stronger. The problem is they had become the boy who had cried wolf, they kept telling Hitler this was the last time. We are going to war if you do this thing we keep telling you not to do.

Certainly quite possible.

That and a nickel would buy you a cream soda.

One factor that I don’t think has been mentioned is that Britain and France weren’t expecting Poland to collapse within five weeks. The pre-war expectation was that Poland would be able to resist for months or even years and would therefore be a second front diverting German resources and Britain and France pushed from the west.

This was, again, based on too strong a reliance on World War I as a model for how World War II would be fought. People thought that armies fighting defensively had a strong advantage over armies fighting offensively.