> Can anybody explain to me how British & France culture felt about colonialism post-WWII? Especially for France [...] they resist Algeria separating. Why?

The First Indochina War is also relevant and an enlightening example of France's post-WWII colonialism. And it lead to the Vietnam War.

As for Britain, apparently at least some factions, such as Churchill and some conservatives, favored the continuing existence of the British Empire and its colonies. It's so odd, looking at it with modern eyes, that the people who fought against the expansionism of Nazi Germany themselves thought it was their right to keep an empire with colonies. It would seem the "free" world wasn't free for everyone.