Short answers, pulled from the story.
Chiang Kai-shek accepted his post as commander-in-chief of the National Revolutionary Army in a ceremony on the 9th of July 1926. This marked the formal start of the Northern Expedition although military clashes had already been ongoing.
Wu Peifu occupied northern Hunan, Hubei, and Henan provinces while Sun Chuanfang controlled Fujian, Zhejiang, Jiangsu, Anhui, and Jiangxi provinces. Zhang Zuolin led the most powerful coalition controlling Manchuria, Shandong, and Zhili.
Hundreds of communists in Shanghai were arrested and killed on the orders of Chiang Kai-shek with Green Gang underworld groups assisting in killing trade unionists and communists within the city. This disturbance became known as the Shanghai massacre effectively ending the alliance between nationalists and communists.
During the course of the incident starting on the 8th of May 1928, the Japanese killed KMT foreign affairs commissioner Cai Gongshi several diplomats and about five thousand Chinese civilians. The conflict began after Chiang Kai-shek arrived on the 2nd of May 1928 to negotiate a Japanese withdrawal from Jinan.
The resumption of the Northern Expedition was officially launched by Chiang Kai-shek on the 7th of April 1928. The NRA First Collective Army rushed into Shandong along the Tianjin Pukou railway capturing Tengzhou by the 16th of April.