Which event motivated the opposing parties of china to fight together?

in 1931, the invasion of manchuria persuaded the chinese party and the warlords to unite with the kuomintang to defeat the foreign enemy.

option 1:

1. british
2. russian
2. japanese

option 2:

1. communist
2. democratic
3. rationalist

In 1931, the Japanese invasion of Manchuria persuaded the Chinese Communist Party and the warlords to unite with the Kuomintang to defeat the foreign enemy.

Japan, Communist

Explanation:

Japan invaded Manchuria in 1931 immediately after the Mukeden incident and installed Manchuko state. The Japanese army invaded Manchuria as it claimed that Chinese lieutenant has destroyed the South Manchuria Railway by detonating dynamite. The imperial Japanese army responded with a full invasion. Mukuden event was a staged incident used as a pretext for invasion. The invasion caused a truce between the Kuomintang and communist party of china,  they cooperated against the Japan.

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