In 1917, Duan took part in suppressing another attempt to restore the monarchy, and spearheaded China's involvement in the First World War on the side of the Allies.

His secret dealings with the Japanese (including the 1918 Sino-Japanese Joint Defence Agreement) later came to light which, along with the Treaty of Versailles's decision to transfer Shandong to Japan, paved way for the May Fourth Movement in 1919.

In 1885 Duan Qirui entered Tianjin Military Academy (天津武備學堂), specializing in artillery, and graduated at the top of his class.

[1] After graduation, he was sent to Lüshun to oversee the construction of artillery fortifications and came to the attention of Li Hongzhang, who sent him to study military science in Germany for two years.

In 1906 he was appointed director of the Baoding Staff College, which allowed him to begin recruiting his own clique of loyal junior officers.

One of the main problems was that Duan began to amass influence over the Beiyang Army as minister of war, thereby undermining Yuan's own control over the soldiers.

Realizing his growing power, Duan became more independent and gradually challenged the President over appointments and reforms in the military.

As Duan fell sick in late 1914, he was unable to stop the President's plans, and he was thus dismissed as minister of war in May 1915.

Yuan's attempt to establish his own dynasty had destroyed the unity of China, and many provinces had achieved de facto independence from Beijing as early as 1915.

Duan served under Li as premier, but dominated him—and the rest of the government—and ruled for a time as the effective dictator of northern China, challenged mostly by semi-independent warlords.

[11] Eventually Feng was able to persuade Duan to relent and the dissident government in the south agreed to dissolve itself when Parliament was reconvened.

In spite of this, Duan's right-hand man and Cabinet Secretary, Xu Shuzheng, issued orders on his own initiative to launch an attack on Hunan.

[12] At this juncture a monarchist general, Zhang Xun, marched his army into Beijing and announced the restoration of the Qing dynasty on July 1, 1917.

[7] Outraged, the other Beiyang generals, led by vice-president Feng Guozhang, mobilized their forces and ended the short-lived restoration attempt.

Duan's strategy now was to negotiate financial loans with Japan, in exchange for concessions, to fund a military buildup for the conquest of the south.

[10] With the poor state of the government's credit and European wartime expenses making both Western and domestic financing impossible, he secretly negotiated the first of the Nishihara Loans with Japan on September 29, 1917.

[13] After Feng Guozhang had restored him as premier, Duan Qirui quickly began preparations to mobilize troops for conquest of the south.

[14] Duan dispatched two former subordinates of Feng Guozhang to the south to conquer Hunan, the linchpin of central China; one of these commanders was Wu Peifu.

He also ordered Zhang Zuolin, military ruler of Manchuria, to send troops to Beijing as a ploy to further pressure Feng to restore him to the premiership.

[15] President Feng Guozhang's term expired on October 10, 1918; in an attempt to placate the south, he agreed not to seek re-election provided Duan also vacate the office of premier on the same day.

[16] When the Nishihara Loans were exposed, along with the secret treaty between the Allies and Japan to transfer Shandong to the Japanese, at the Versailles peace conference, Beijing and the rest of the nation exploded in protest in what came to be known as the "May Fourth Movement" on May 4, 1919.

[17] However, there was extensive opposition across China to return to imperial monarchy, and as a show of force, Duan Qirui ordered a Caudron Type D aircraft, piloted by Pan Shizhong (潘世忠) and bombardier Du Yuyuan (杜裕源) from Nanyuan airbase to drop three bombs over the Forbidden City, causing the death of an eunuch, but otherwise minor damage.

Although Duan's army had been equipped and trained by Japan, it succumbed easily to Wu Peifu-led Zhili forces and their allies.

Other Anhui members secretly mediated between Zhang Zuolin and Feng Yuxiang, an important leader in the Zhili clique, when the latter decided to revolt against his former allies in the Second Zhili–Fengtian War.

Feng Yuxiang's defection resulted in the defeat of Wu Peifu and the Zhili clique and forced them to withdraw to the south.

With his clique's military power in a shambles, Duan's government was hopelessly dependent on Feng Yuxiang and Zhang Zuolin.

The next month Feng Yuxiang again revolted, this time against the Fengtian clique, and deposed Duan, who was forced to flee to Zhang Zuolin for protection.