The fall of the British empire surely had its roots in the reason for the existance of it, money in profits and especially in taxation.
The loss of the North American colony lay with taxation (or perhaps lack of democracy if you prefer)
The British empire was hugely over-extended with its wars around the world and it needed money.You pretty much know what happened next.
When it elected to hang on to the Indian subcontinent, where it resumed its taxation policy, using the local hierarchy as the collection system and leave North America, the change it started there in political thinking would spread around the world, and it’s the right to self-determination and democracy that sealed the fate of the British Empire.
Ok so many former colonies are not democratic, but the belief that the local population had its own right to govern itself is what led to the downfall o the Empire.
The idea of local democracy had either to be crushed, or it would inevitable destroy the British Empire, but since the North American colony was a step too far for British control, the result seems fairly inevitable to me.