Yan Xishan in the context of "Romanization of Chinese"

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.

Suiyuan (simplified Chinese: 绥远; traditional Chinese: 綏遠; pinyin: Suíyuǎn; lit. 'Pacify the Distant Region') was a historical province of China. Suiyuan's capital was Guisui (now Hohhot). The abbreviation was 綏 (pinyin: suí). The area Suiyuan covered is approximated today by the prefecture-level cities of Hohhot, Baotou, Wuhai, Ordos, Bayan Nur, and parts of Ulanqab, all today part of Inner Mongolia Autonomous Region. Suiyuan was named after a district in the capital established in the Qing Dynasty.

In the early 1930s Suiyuan was occupied by the Shanxi warlord Yan Xishan, who mined Suiyuan's iron, reorganized the province's finances, and brought over 4,000 acres (16 km) of land under cultivation for the first time. Most of the work and settlement of Suiyuan at this time was done by Shanxi farmer-soldiers under the direction of retired officers from Yan's army. Yan's control of Suiyuan was sufficient to cause one visiting reporter to refer to Suiyuan as a "colony" of Shanxi.

The Central Plains War (traditional Chinese: 中原大戰; simplified Chinese: 中原大战; pinyin: Zhōngyúan Dàzhàn) was a series of military campaigns in 1929 and 1930 that constituted a Chinese civil war between the Nationalist Kuomintang government in Nanjing led by Generalissimo Chiang Kai-shek and several regional military commanders and warlords who were former allies of Chiang.

After the Northern Expedition ended in 1928, Yan Xishan, Feng Yuxiang, Li Zongren and Zhang Fakui broke off relations with Chiang shortly after a demilitarization conference in 1929, and together they formed an anti-Chiang coalition to openly challenge the legitimacy of the Nanjing government. The war was the largest conflict in the Warlord Era, fought across Henan, Shandong, Anhui and other areas of the Central Plains in China, involving 300,000 soldiers from Nanjing and 700,000 soldiers from the coalition.