Short answers, pulled from the story.
The Chinese Communist Party was founded on the 23rd of July 1921 in Shanghai at the 1st National Congress of the CCP. The party started with only 50 members before growing to 2,428 by 1925.
Chiang Kai-shek ordered a massacre of Communists in Shanghai on the 12th of April 1927 which spread nationwide as the White Terror. This event led to the death of tens of thousands of Communists and caused the loss of approximately half its members.
The Long March was a 9,000 kilometer retreat from South China to Northern China that began after the fourth encirclement campaign disaster. The CCP paused this march in January 1935 to hold the conference in Zunyi where Mao Zedong denounced previous leadership strategies.
Japanese army occupied Manchuria in 1931 triggering debates about whether the Nationalist Government should declare war on Japan. Chiang Kai-shek policy of non-resistance contributed to decrease in support for Nationalists and increase in support for the Chinese Communist Party.
Chairman Mao Zedong officially proclaimed the founding of the People's Republic of China on the 1st of October 1949 at Tiananmen Square Beijing. This ceremony included a military parade involving around 16,000 PLA officers and personnel.