With the assistance of allied warlords, including Yan Xishan and Feng Yuxiang, nationalist forces secured a series of decisive victories against the Beiyang Army.

Since the conclusion of the Constitutional Protection Movement in 1922, the KMT had been bolstering its ranks to prepare for an expedition against the northern warlords in Beijing, with the goal of reunifying China.

Before his death in March 1925, Sun Yat-sen, the founder of the Republic of China and co-founder of the KMT, was supportive of Sino-Soviet co-operation, which had involved forming the First United Front with the Chinese Communist Party (CCP).

[22] Concerns about the rising power of the leftist faction, and the effect of the strike on the Guangzhou government's ability to raise funds, which was largely dependent on foreign trade, led to increasing tensions within the United Front.

[23][24] In the aftermath of the coup, Chiang negotiated a compromise whereby hardline members of the rightist faction, such as Wu Tiecheng, were removed from their posts in compensation for the purged leftists.

[19] Amidst heavy fighting along the border between KMT-held territory and that of the recently allied forces of the Fengtian and Zhili cliques, the nationalist government appointed Chiang Kai-shek commander-in-chief of the NRA on 5 June 1926.

[28][29] The initial strategy for the KMT's northern advance against the Zhili warlords, which was largely devised by Soviet advisors Mikhail Borodin and Vasily Blyukher, was to focus on defeating Wu Peifu and appeasing Sun Chuanfang, while ignoring Zhang Zuolin of the Fengtian clique.

[30][28][29] Having switched from a defensive to offensive posture, KMT forces quickly advanced from their base in Guangdong into Wu-controlled Hunan province, capturing Changsha on 11 July.

[32][33] Whilst the Fengtian clique had offered its support to Wu, he refused their aid, fearing that the northern warlords would undermine his position if he allowed their troops into his territory.

[34] At a military conference held in Changsha on 11–12 August, the KMT decided to launch a direct assault on Wu's stronghold of Wuchang, bypassing Sun's Nanchang.

Sun retook most of the territory he had lost, brutally reasserting his authority by killing hundreds of students, teachers, and suspected members of the KMT, whose severed heads he displayed on spikes in public places.

[45] With the Northern Expedition's advance halted, Chiang wired the government in Guangzhou, demanding an end to the still ongoing Canton–Hong Kong strike, which continued to hamper his supply chain.

[39] As bloody fighting continued in Jiangxi, the civil governor of Zhejiang province, Xia Chao, one of Sun's subordinates, defected to the KMT government in Guangzhou.

With his forces in disarray, Sun's commander in the area, Meng Chao-yueh, decided on 17 February to abandon Hangzhou and flee with his 20,000 troops by train to Jiangsu province.

[61] The Fengtian clique responded to Sun's plea for help by reinforcing Jiangsu and Anhui provinces, while increasing the number of troops in Henan in support of Wu Peifu.

Communist-led trade unions staged near-constant demonstrations in Wuhan itself, and across the nominally KMT-controlled territories, establishing parallel structures of administration in areas liberated by the NRA.

Mikhail Borodin, the official liaison between the KMT and the Soviet government in Moscow, had spent years cultivating this alliance, while covertly encouraging CCP expansion.

[76] This Soviet-backed leftist wing of the KMT came to dominate the nationalist government in Wuhan, which increasingly directed its ire at NRA commander-in-chief Chiang Kai-shek.

On 1 April, the Wuhan government, advised by Borodin, issued edicts stripping Chiang of his authority in foreign affairs, financial matters, and communications, and ordered that he leave his command post in Shanghai and go to the front.

[77] The government intended to send a small force to Nanjing with the aim of "disarming" Chiang, but put that plan on hold following Wang Jingwei's return from exile in Europe.

Li Zongren's NRA Seventh Army managed to drive the NPA away from the railway briefly, but thousands more of Sun's troops, including White Russian mercenary units, crossed the river the next day and retook the station, cutting off contact between Nanjing and Shanghai.

Wang Jingwei refused to join the new government, as did Tang Shengzi, who became an independent warlord in his own right, controlling Hubei, Hunan, Jiangxi, and parts of Anhui.

[104] On the other hand, Shanxi warlord Yan Xishan, theretofore independent, aligned his province with the Nanjing government, adding 100,000 troops to NRA ranks and increasing the pressure on Zhang Zuolin.

[112][113] With the frigid winter of northern China prohibiting any further advance, Chiang used the months following his reappointment to consolidate his control and restore the integrity of the Nanjing administration.

Zhang, weary of KMT propaganda that linked him with the Japanese massacre at Jinan, responded that he would "not recognize Japan's interest in Manchuria", compromising his position.

The Shandong–Zhili Army led by Zhang Zongchang and Chu Yupu refused to surrender, and despite the defeats it had suffered still numbered about 60,000–70,000 soldiers, as well as at least three armoured trains manned by White Russian mercenaries under General Konstantin Nechaev.

[138][139][140][141][142] Zhang Xueliang officially declared his allegiance to the nationalist government in Nanjing on 29 December 1928, marking the formal end of the Northern Expedition, and the reunification of China.

Chiang desired to take the power that had been executed through various provincial entities and concentrate it in the central government, in an effort to curtail the provincialist tendencies of the warlord era.

[149][150] Defeated warlord Zhang Zongchang would return to his former territory of Shandong in 1929, where he launched a rebellion against his former subordinate Liu Zhennian, who had defected to the nationalists during the Northern Expedition.

[154] Stalin, who in his China strategy prohibited the arming of workers and peasants, and encouraged co-operation with the bourgeoisie, was considered vulnerable in the aftermath of the failure of the first United Front.