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In 1949, the Chinese Communist Party and it's armed wing, the People's Liberation Army, were on the cusp of throwing the Nationalists out of mainland China. Their last major stronghold was Nanjing, across the Yangtze River.

Behind the scenes, Mao Zedong was in something of a feud with Joseph Stalin. Stalin's actions in regards to China such as verbally supporting the Nationalist regime and ordering the Communists to abandon captured territory in the northern China had greatly frustrated and infuriated the higher echelons of the CCP. This seemingly hostile behavior was rooted in Stalin's belief that the Communists could never control all of China, he much less desired such an outcome. In his view, a united, communist China was a far greater threat to the Soviet Union than the ineffective regime of Chang kai-Shek.

To this end, he encouraged reconciliation between the Nationalists and Communists. All efforts to this end were slapped away by Mao Zedong.

in summer 1949, as the PLA was about to cross into Southern China and in a final attempt to intimidate Mao, he ordered Mao not to cross the Yangszte River under the threat of American military involvement. Instead, Stalin proposed a partitioned China, with the dividing line being the aforementioned Yangtze River. Under this proposal, the CCP would occupy the North while the ROC would occupy the south.

As to what happened next, I will let Mao Zedong explain it.

"When we were about to cross the Yangtze River, Stalin still wanted to prevent us. According to him, if we did so, America would send troops to China. I did not listen to what he said. We crossed the Yangtze. America did not send troops",

But what if the Americans did send troops to China after the Communists crossed the Yangtze and they pushed the Communists back so much that the CCP agreed to Stalin's proposal and partitioned China along the Yangtze River?
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