The Rise of the Second Mongolian Empire

A few things . . .

Korea (Joseon) was united before 1910, and when Japan annexed it and made it into a colony, it still remained united.

Taiwan was annexed by Japan in 1895, and Manchuria (Manchukuo) was also annexed in 1932.

It's hard to imagine Mongolia conquering East Asia in your scenario. For one thing, Mongolia is a desert country, and Tibet is a mountainous country, so it would almost be a miracle for Mongolia to adapt to drastically different terrain. Even if Chinese refugees emigrated to Mongolia, most of them would be civilians, and not soldiers, so Mongolia would have a hard time conquering China, because China had 4.3 million soldiers in the Chinese Civil War. On the other hand, Mongolia only had 60,000 at its height, which makes a stark comparison.

In order to make the timeline more plausible, Mongolia should industralize in either the 18th or 19th century by accepting Europeans and adapting to their models. It could then make a pre-emptive invasion in the 19th century by taking Manchuria, and possibly Xinjiang. The Qing would be unable to respond because of their involvement in the Taiping Rebellion, Opium Wars, and the Boxer Rebellion. They would also be severely demoralized because the Manchus were located in Manchuria. Mongolia then could utilize propaganda to persuade millions of Chinese refugees to cross the border, greatly increasing the population. They could then train some of the population for 50 years, then attack and conquer either most or all of China, and Korea.

I think you're confusing Mongolia with Japan. The Meiji government did industralize in 20-30 years, but they had a military of 650,000 in the early 1900's, and more than 6 million by 1945, which was more than that of China.

This situation could be compared to a country in Africa dominating Europe. Both scenarios are possible, but it would take 100-200 years for them to prepare for the conquests.
 
Perhaps you are right I'm going to put this scenario on temporary hold for two reasons. 1, I'm thinking about how to make it more plausible. 2, I've had an idea for another timeline.
 
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