[Right_Wing_Madman]

Why did Britain and France and the USSR need US supplies, weapons and financing in 1943-45?

Because unlike Germany, Britain and France failed to maintain and rebuild their militaries after World War I.

[dfwgator]

Because unlike Germany, Britain and France failed to maintain and rebuild their militaries after World War I.

You should have seen our military around 1938.

[buwaya]

You are missing the point.
The UK, France, and the USSR required US aid while they were already winning. They had insufficient resources of their own to keep up maximum pressure on the enemy, to bring the war to a swifter conclusion.