[Britain has foreign entanglements that force it to take Russia and China seriously as threats, plus as an island nation we depend very heavily on the sea for raw materials to fuel our economy.]
Russia’s gdp is less than Italy’s, both Britain and France could utterly outclass Russia militarily if we were willing to pay the same percent of gdp that the Russians do. Its kind of ridiculous Russia has as much geopolitical power as it does when it is economically speaking, a minnow on the world stage.
As for Empire, I think the writing was on the wall regardless of what the Americans did. Britain and France were both exhausted from the war effort and pro-independence movements were gathering strength, now aided by the communists in Russia. Decolonisation was inevitable. In the case of the British Empire this was the long term plan anyway, once each colony had reached the stage were it was considered to be ready for ‘responsible’ self government.