The decline in support for Chiang Kai Shek and the Kuomintang

Why did Chiang and the Kuomintang become unpopular?

Losses in the Sino-Japanese War

During the Sino-Japanese War, the KMT used conventional warfare against the Japanese, and as a result, they suffered heavy casualties.

The KMT did have some support from the USA, which made their military technology superior to the CCP, however it was still inferior to the Japanese who had superior tanks and weapons.

Failure against the Communists

In the end, Chiang Kai Shek's government failed despite help from the USA and even the USSR.

Despite this, the main reason is that the USA wanted a strong KMT so they could resist Japanese aggression.

They did not believe the CCP was strong enough to rule China as a central government by themselves.