The Northern Expedition was a military campaign launched by the National Revolutionary Army (NRA) of the KMT, also known as the "Chinese Nationalist Party", 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 Xinhai Revolution of 1911.

Clashes broke out such as the Shanghai Massacre of 12 April 1927, which was an example of the violent suppression of Chinese Communist Party organizations and leftist elements that took place in Shanghai by forces supporting General Chiang Kai-shek and conservative factions in the KMT. For the rest of 1927, the CCP would fight to regain power, beginning the Chinese Civil War. With the failure and the crushing of the Guangzhou Uprising at Guangzhou however, the Communist power was largely diminished, unable to launch another major urban offensive.

The Nanchang Uprising was the first major Nationalist Party of China""CCP engagement of the Chinese Civil War, begun by the Chinese Communists to counter the Shanghai Massacre of 1927 by the KMT.

Diplomatic efforts to build relations with the rest of the world were developed and continued after the Nanjing Decade. Banking reforms were established, and public health facilities were upgraded and created. The legal and penal system was brought up to the standards exercised by other countries.

However, relations with Japan, in particular, remained strained. The Jinan incident began as a 3 May 1928 dispute between Chiang Kai-shek's NRA and Japanese soldiers and civilians. Shortly after, the Fengtian warlord Zhang Zuolin was assassinated near Shenyang on 4 June 1928 in what became known as the Huanggutun Incident.

Japan was not the only nation with sizable interests in Manchuria. The Soviet Union had extensive lumber interests, among others, in the eastern part of the territory, and they, too, experienced some of the same difficulties as the Japanese. In 1928, Zhang Xueliang and the Soviet Union went to war over control of the Chinese Eastern Railroad, which brought resources from China and Manchuria to the Soviet Union. This large-scale conflict alarmed the Japanese, who wanted to avoid any interruption in their supplies, but it also showed them the weaknesses of the Chinese and warlord forces in the area. Additionally, the assertion of control by the Soviets in the western part of the territory alarmed the Japanese, who saw the possibility of eventual Soviet movement into their zone of control, which would not only threaten their economic interests but also bring communism that much closer to Japan itself.

China made a business deal with Japan to build and manage the South Manchuria Railway. It was a prosperous arrangement for both countries. However, in September of 1931, there was an explosion that led to events referred to as the Mukden Incident. The Mukden Incident, or Manchurian Incident, was actually a ruse staged by Japanese military personnel as a pretext for the 1931 Japanese invasion of Manchuria. The ruse was exposed by the Lytton Commission of 1932, leading Japan to diplomatic isolation and its March 1933 withdrawal from the League of Nations. The bombing act is known as the Liutiao Lake Incident. The Empire of Japan's Kwantung Army invaded Manchuria on 18 September 1931, immediately following the Mukden Incident. At the war's end in February 1932, the Japanese created a puppet state with the Establishment of Manchukuo. The January 28 Incident or Shanghai Incident was a conflict between the RoC and the Empire of Japan.

The Long March at the end of 1934 was a year-long military retreat undertaken by the Red Army of the CCP, the forerunner of the People's Liberation Army, to evade the pursuit of the NRA/KMT).

The December 9th Movement was a mass protest led by students in Beijing on December 9, 1935, to demand that the Chinese government actively resist Japanese aggression.

The Xi'an Incident, was a political crisis that took place in Xi'an, Shaanxi in 1936. Chiang Kai-shek, leader of the Nationalist government of China, was detained by his subordinate generals, Zhang Xueliang and Yang Hucheng, in order to force the ruling KMT to change its policies regarding the Empire of Japan and the CCP.

Because Japan had been helping China upgrade its industrial base, it was well aware of the fact that China was behind other countries in terms of modernization. Japan craved the resources and opportunities China held so they could expand their own sphere of influence in the Pacific region. The Mukden Incident had presented them with a golden opportunity, as the Japanese could use Manchuria as a base in order to take over China.

The Second Sino-Japanese War spanned a number of conflicts between 1937 and 1945 during which the internal civil war between communists and nationalists was suspended with the creation of the Second United Front. This was a tenuous union, but one that was needed because Japan was their mutual enemy and a great threat to China.

There were a number of major incidents and battles during the period of the Second Sino-Japanese War