Your curiosity seems endless, MM.
I sometimes forget your age
Building up a new Chinese Empire was a major premise for Japanese to invade like Mongolians and Manchurians did in their old times.
Japanese settlers in Manchukuo were already happy to speak Chinese and accept the local culture.
If everything had gone well, the country of Japan would have been disappeared to be a part of China in the 21st century.
The term "China" originally means "The center of the world" to be adored by Asians.
So, it was a simple story.
So in the long term, the US economy would have benefited from supporting Japan's expansion, the Western colonies need not have been invaded, stability brought to a long unstable China and a greater ability by the West to contain Germany, Italy and the USSR.