Is it true that WW2 France and Britain declared war on Germany even though they were fully aware that Germany had no intention of attacking them?

I'm Russian and allergic to war, my country just invaded Ukraine and it looks like we're really losing - thousands of our guys are dying, our economy is in shambles, and there's no end in sight.<br><br>So I'm interested to know - what mistakes should we avoid, judging by historical experience?<br><br>I've heard that in WW2 France and Britain declared war on Germany even though they were fully aware that Germany had no intentions of attacking them - Hitlers Drang nach Osten (Drive to the East) manifestly stated that the Reich's expansion efforts would be focused on Eastern Europe and even the Soviet Union, whereas Western Europe was seen as a valuable trading partner and ally, as witnessed by the Molotov-Ribbentrop Pact and the Munich Betrayal.<br><br>What were they thinking?