They only made gains because they were mobilized for war and their enemies weren't. That means they had an advantage for a little while, but they lacked the ab

They only made gains because they were mobilized for war and their enemies weren't. That means they had an advantage for a little while, but they lacked the ability to completely defeat the US, USSR, and UK, so they were bound to be defeated once those three countries converted the full weight of their economies to military purposes. Quitting while they were ahead was not an option, unless by "quitting" you mean "surrender."