What was the decisive respective *moments* where empires like Roman, Ottoman, British, "fell"?

https://lemmy.world/post/44467232

What was the decisive respective *moments* where empires like Roman, Ottoman, British, "fell"? - Lemmy.World

It probably happened over a long period of course but when did the ref know when to “call it”?

Historically, the suez crisis 1956 was the final nail in the coffin for the British empire symbolically. The pound crashed and lost alot of influence in the middle east

It has a lot of parallels to this crisis war in iran right now.