"Show me just what Mohammed brought that was new, and there you will find things only evil and inhuman, such as his command to spread by the sword the faith he preached." - Manuel II Palelologus
Korea makes a better comparison. It took four or five years to bring the South Korean forces up to the point where they could hold the line. We were of course able to start drawing down after the Armistice. That was three years after the war started. But the lesson is that you don’t just pick up and leave and besides, we were close by in Japan.