Jinan incident (1928).

At the time, China was in the middle of the Northern Expedition, a campaign led by the Kuomintang (KMT) under Chiang Kai-shek. The goal was to unify China by defeating regional warlords.
Japan, meanwhile, had significant economic and strategic interests in Shandong province and maintained troops there to protect its citizens and influence.

As Nationalist forces advanced northward and approached Jinan Japanese troops were already stationed in the city. Tensions rose between Japanese forces and the incoming Chinese Nationalist army. Fighting broke out in early May 1928.
The exact trigger is disputed, but the conflict escalated quickly: Japanese forces engaged Chinese troops and civilians. There were reports of killings of Chinese soldiers and noncombatants.
The Chinese side was militarily weaker in this encounter and eventually withdrew.

Fighting took place within the city rather than on open battlefields. Many civilians were affected, contributing to anti-Japanese sentiment in China.
Relations between China and Japan worsened significantly.

Japan consolidated its control over parts of Shandong.
The incident intensified Chinese nationalism and distrust of Japan.
It is often seen as a precursor to larger conflicts, including the Second Sino-Japanese War.