If memory serves, just a bit further south the ports are ice free. Russia had a port in Lüshunkou (then called Port Arthur). It is just west of Korea, and without ice. It was the subject of the Russo-Japanese war.
While looking that up I also saw that the Ming dynasty banned Han chinese from settling in the north for 300 years. So, that likely also had an impact.
During the first two centuries of the Manchu Qing Dynasty, this part of China, the traditional homeland of the ruling Manchus, was, with few exceptions, closed to settlement by Han Chinese civilians, with only certain Manchu Bannermen, Mongol Bannermen, and Chinese Bannermen allowed in.
https://travel.stackexchange.com/questions/79051/is-the-port...
If memory serves, just a bit further south the ports are ice free. Russia had a port in Lüshunkou (then called Port Arthur). It is just west of Korea, and without ice. It was the subject of the Russo-Japanese war.
While looking that up I also saw that the Ming dynasty banned Han chinese from settling in the north for 300 years. So, that likely also had an impact.