You will read a lot about the large military hardware manufacturing facilities, aircraft, ships, tanks, etc. But one of the things that was done was to decentralize war production. Europe and England simply couldn't do that as well as the US and Russia. It's simply a matter of geography.
When Russia's manufacturing was threatened by Nazi bombing and invasion, they simply picked it up and moved it further away. Yes, they still needed US made war materials. But then so did every other single ally.
But Germany and to a lesser extent Italy did have manufacturing outside of their borders. Although it was recovering from civil war, economic depression and famine, Spain provided war materiel to the Axis. As did other "silent allies", Portugal and Sweden (neutral countries supply to both sides of a conflict or none, not just one).
