quality:correction, information:filtering, stylistic:style_transfer, structural:expansion
Republican era

In 1919, after World War I, the Japanese took over the German sphere of influence in Shandong, including control of the Jiaoji railway, and established a significant Japanese influence in Jinan. According to estimates by a contemporary Japanese government official, about 2,000 Japanese were living in Jinan in 1931, about half of whom were involved in the opium trade for which the Japanese had a loosely controlled monopoly that was exploited with the participation of Chinese traders.

During the Warlord era of the Republic of China, Zhang Zongchang, nicknamed the "Dogmeat General", ruled Shandong from Jinan for a period that lasted from April 1925 until May 1928. Zhang was unpopular for his heavy-handed rule and in particular his heavy taxation. Besides heavy taxes, he relied financially on opium to finance his periodic wars. Zhang even planned to use some of the wealth extracted from these sources for building a living shrine and a large bronze statue for himself on the shore of Daming Lake, but these plans were not realized as his rule came to an end.

In the spring of 1928, the Kuomintang 's Northern Expedition reached Jinan. On May 3, 1928, clashes developed between Japanese troops stationed in Jinan and the Kuomintang troops moving into the city (Jinan incident). Cai Gongshi, a Kuomintang emissary sent to negotiate and 16 members of his entourage were cruelly executed by the Japanese. Japanese officers placed an order to slice off his nose and ears, and to gouge out his eyes and tongue. Sixteen other members of his negotiation team were also striped naked, recklessly whipped, dragged to the back-lawn, and slaughtered by machine guns on the same day. After the incident, Japanese reinforcements were sent to Shandong and by 11 May, Japanese troops pushed the Chinese troops from the area, inflicted thousands of casualties and killed over 2000 Chinese civilians. The Japanese occupied Jinan for more than six months until they withdrew to their garrison in Qingdao on 28 March 1929. When Chiang lectured a group of Chinese army cadets, he urged them to turn their energies to washing away the shame of Jinan, but to conceal their hatred until the last moment. The Kuomintang government later decreed that May 3 be designated a "National Humiliation Memorial Day."

During the Nanjing decade of the Republic of China, Han Fuju, a military commander from the warlord era who had aligned himself with the Kuomintang, was rewarded with the military governorship of Shandong, after fighting against the rebel troops of Yan Xishan and his former commander Feng Yuxiang in the Central Plains War in 1930. He established his base in Jinan and is credited with curtailing banditry and drug trading, thereby bringing a measure of peace and prosperity to the city. However, from 1935 onwards Han was under heavy pressure from the Japanese consul in Jinan to declare Shandong an "independent state" allied with Japan.

After the start of the Second Sino-Japanese War, the Japanese invasion force crossed the Yellow River 60 km (37 mi) north-east of Jinan on December 23, 1937. Han Fuju abandoned Jinan the next day against orders to hold the city to the death. He ordered the offices of the provincial government and the Japanese consulate in Jinan to be burned down and the ensuing power vacuum led to widespread looting in the city. Japanese troops from the 10th Division of the Manchurian Area Army entered Jinan on December 27, 1937. Han Fuju was arrested and executed for disobeying orders from superior commanders and retreating on his own accord by Chiang Kai-Shek's chief of staff, General Hu Zongnan.