Zhang Zuolin in the context of "Warlord"

The Warlord Era was the period in the history of the Republic of China between 1916 and 1928, when control of the country was divided between rival military cliques of the Beiyang Army and other regional factions. It began after the death of Yuan Shikai, the President of China after the Xinhai Revolution had overthrown the Qing dynasty and established the Republic of China in 1912. Yuan's death on 6 June 1916 created a power vacuum which was filled by military strongmen and widespread violence, chaos, and oppression. The Nationalist Kuomintang (KMT) government of Sun Yat-sen, based in Guangzhou, began to contest Yuan's Beiyang government based in Beijing for recognition as the legitimate government of China.

The most powerful cliques were the Zhili clique led by Feng Guozhang, who controlled several northern provinces; the Anhui clique led by Duan Qirui, based in several southeastern provinces; and the Fengtian clique led by Zhang Zuolin, based in Manchuria. The three cliques often engaged in conflict for territory and hegemony. In mid-1917, after Yuan's successor Li Yuanhong attempted to remove Duan as premier, the general Zhang Xun forced Li to resign and made a brief attempt to restore the Qing dynasty, which was quashed by Duan's troops. Feng became the acting president, but was forced to step down by Duan in late 1918 and was replaced by Xu Shichang. In mid-1920, the new Zhili clique leaders, Cao Kun and Wu Peifu, defeated Duan in the Zhili–Anhui War in an alliance with Zhang Zuolin. A power struggle broke out between Cao and Zhang which ended with Cao's victory in the First Zhili–Fengtian War in 1922. Cao was president until 1924, when during the Second Zhili–Fengtian War he was betrayed by his subordinate Feng Yuxiang, who joined with Zhang to stage a coup against Cao. Feng and Zhang shared power and recalled Duan to serve as president before Zhang removed them both in 1926; in 1927, he declared himself Generalissimo.

The Northern Expedition was a military campaign launched by the National Revolutionary Army (NRA) of the Kuomintang (KMT) against the Beiyang government and other regional warlords in 1926. The purpose of the campaign was to reunify China, which had become fragmented in the aftermath of the 1911 Revolution. The expedition was led by Generalissimo Chiang Kai-shek, and was divided into two phases. The first phase ended in a 1927 political split between two factions of the KMT: the right-leaning Nanjing faction, led by Chiang, and the left-leaning faction in Wuhan, led by Wang Jingwei. The split was partially motivated by Chiang's Shanghai Massacre of Communists within the KMT, which marked the end of the First United Front. In an effort to mend this schism, Chiang Kai-shek stepped down as the commander of the NRA in August 1927, and went into exile in Japan.

The second phase of the Expedition began in January 1928, when Chiang resumed command. By April 1928, the nationalist forces had advanced to the Yellow River. With the assistance of allied warlords, including Yan Xishan and Feng Yuxiang, the nationalist forces secured a series of decisive victories against the Beiyang Army. As they approached Beijing, Zhang Zuolin, leader of the Manchuria-based Fengtian clique, was forced to flee and was later assassinated shortly thereafter by the Japanese. His son, Zhang Xueliang, took over as the leader of the Fengtian clique, and in December 1928, announced that Manchuria would accept the authority of the nationalist government in Nanjing. With the final piece of China under KMT control, the Northern Expedition concluded successfully and China was reunified, heralding the start of the Nanjing decade.

The Fengtian Government (Chinese: 奉系军阀; pinyin: Fèngxì Jūnfá; Wade–Giles: Feng-hsi Chün-fa) was the faction that supported warlord Zhang Zuolin during China's Warlord Era. It took its name from Fengtian Province, which served as its original base of support. However, the clique quickly came to control all of the Three Northeastern Provinces. The clique received support from Japan in exchange for protecting Japanese military and economic interests in Manchuria. The Fengtian Army frequently intervened in many of the conflicts of the Warlord Era.

Following the Zhili–Anhui War of 1920 and 1921, the Fengtian and Zhili cliques exercised joint control of Beijing and the Beiyang Government. Tensions soon began building between the two, resulting in clashes for control of Beijing known as the First Zhili–Fengtian War (1922). The Second (1924) Zhili–Fengtian War started later over the Zhili invasion of the remnants of the Anhui clique, which had become allies of the Fengtian Clique, which resulted in a Fengtian victory, with the Zhili clique retreating as far south as Henan. The power of the Fengtian Clique began to decrease in the midst of the Kuomintang's Northern Expedition. In 1928, while he was retreating North, Zhang Zuolin's Japanese sponsors blew up his train, killing him. After Zhang's assassination, his son, Zhang Xueliang, took over the leadership of the clique. He preferred to work with the Kuomintang rather than the Japanese and symbolically pledged allegiance to the Nationalist Government in Nanjing. In practice, the Fengtian clique continued to independently govern Manchuria until the Japanese invasion in 1931.

The First Zhili–Fengtian War (First Chihli-Fengtien War; simplified Chinese: 第一次直奉战争; traditional Chinese: 第一次直奉戰爭; pinyin: Dìyīcì Zhífèng Zhànzhēng) was a 1922 conflict in the Republic of China's Warlord Era between the Zhili and Fengtian cliques for control of Beijing. The war led to the defeat of the Fengtian clique and the expulsion of its leader, Zhang Zuolin, from the coalition Zhili-Fengtian government in Beijing. Wu Peifu was credited as the strategist behind Zhili's victory.

The Second Zhili–Fengtian War (Second Chihli-Fengtien War; simplified Chinese: 第二次直奉战争; traditional Chinese: 第二次直奉戰爭; pinyin: Dì'èrcì Zhífèng Zhànzhēng) of 1924 was a conflict between the Japanese-backed Fengtian clique based in Manchuria, and the more liberal Zhili clique controlling Beijing and backed by Anglo-American business interests. The war is considered the most significant in China's Warlord era, with the Beijing coup by Christian warlord Feng Yuxiang leading to the overall defeat of the Zhili clique. During the war the two cliques fought one large battle near Tianjin in October 1924, as well as a number of smaller skirmishes and sieges. Afterwards, both Feng and Zhang Zuolin, the latter being ruler of the Fengtian clique, appointed Duan Qirui as a figurehead prime minister. In south and central China, more liberal Chinese were dismayed by the Fengtian's advance and by the resulting power vacuum. A wave of protests followed. The war also distracted the northern warlords from the Soviet-backed Nationalists based in the southern province of Guangdong, allowing unhampered preparation for the Northern Expedition (1926–1928), which united China under the leadership of Chiang Kai-shek.

The Huanggutun incident (Chinese: 皇姑屯事件; pinyin: Huánggū Tún Shìjiàn), also known as the Zhang Zuolin Explosion Death Incident (Japanese: 張作霖爆殺事件, Hepburn: Chōsakurin bakusatsu jiken), was the assassination of the Fengtian warlord and Generalissimo of the Military Government of China Zhang Zuolin near Shenyang on 4 June 1928.

Zhang was killed when his personal train was destroyed by an explosion at the Huanggutun Railway Station that had been plotted and committed by the Kwantung Army of the Imperial Japanese Army. Zhang's death had undesirable outcomes for the Empire of Japan, which had hoped to advance its interests in Manchuria at the end of the Warlord Era, and the incident was concealed as "A Certain Important Incident in Manchuria" (満州某重大事件, Manshu bou judai jiken) in Japan. The incident delayed the Japanese invasion of Manchuria for several years until the Mukden Incident in 1931.