At the beginning of the 20th Century, China was emerging from centuries of rule by the Manchu, the descendants of Mongolian nomads who had conquered the Middle Kingdom in 1644. The new Guomindang (GMD) party was a broad alliance of modernizers.
In the 1920s the GMD gained control in China, making deals with some local warlords but overpowering others. The GMD also cut a deal with the Chinese Communists, which upset the remaining warlords. As GMD control spread over more and more of China, it gradually grew stronger, but also more conservative as Chiang Kai-shek and even the left wing of the GMD marginalized the Communists.
The first few years of Chiang's rule saw substantial progress. But the Japanese were also moving; in 1931 they occupied Manchuria, on China's northern border. Chiang was focused on internal politics, launching a series of campaigns against the Communists (now led by Mao Zedong) which culminated in their "Long March" as they fled to a remote mountainous region in 1934-35.
Chiang was at his strongest in China, but the Japanese were growing increasingly active and clearly looking for an opportunity to grab parts or all of China. Many patriotic Chinese thought the internal turmoil would only help the Japanese.
In 1936 Chiang was visiting Xian and the local warlord, Zhang Xueliang, took him prisoner. But Chiang was treated with courtesy: "I wish to lay my views before Your Excellency" is hardly the way most coup plotters begin. Zhang released Chiang after two weeks, and the GMD formed a shaky common front against the Japanese that lasted through WWII.
The GMD imprisoned Zhang, was taken to Taiwan after the Chinese Civil War and jailed for 54 years. He recently died, and the old warlord was warmly remembered by the Chinese Communists.