The Japanese said they were attacked but it was a ruse to invade
Answer this question…It gave Japan an excuse to retaliate against the Chinese and gain control of Manchuria.
Japan had used an excuse a Chinese Attack on a Japanese Railway near the city of Mukden. In fact, the "Mukden incident" had been carried out by Japanese Soldiers disguised as Chinese.
In 1931, Japan invaded and occupied Manchuria.
Japan was jealous of the rich fertile lands that Manchuria had, they also wanted more land so that the Japanese could expand their empire. They used the Mukden incident as an excuse to invade China as they knew that they would be,like them, suffering from the depression.
Ostensibly Japan sought to redress the wrongs that occurred during the Mukden 'Incident" where part of a railroad was dynamited but the truth was that Japanese militarists (war mongers) used this as an excuse to invade Manchuria .
Japan invaded Manchuria on 19 September 1931. Following the Mukden incident (staged by Japanese spies), Japan's Kwantung Army immediately invaded Manchuria and established a puppet state they names Manchuko.
Japan decided to invade Manchuria the day after the Mukden incident, in 1931. However, the entire state of Manchuria was not conquered until 1932, so the answer to the question is 1932.
mukden incident
Japan , following the Mukden Incident .
The Chinese-Japanese dispute in July 1931 (the Wanpaoshan Incident) . The Japanese invasion of Manchuria began on September 18, 1931, when the Kwantung Army of the Empire of Japan invaded Manchuria immediately following the Mukden Incident. The Japanese established a puppet state called Manchukuo, and their occupation lasted until the end of World War II.
Historians generally accept two incidents involving China in the 1930's with Imperial Japan. The first was the "Manchurian Incident" (Mukden Incident-near a famous Russian-Japanese battle from the 1904-1905 war) which occurred in 1931/1933, depending on your source, which entailed the destruction a railroad track in Manchuria, triggering a Japanese military response. The second incident, occurred at or near the "Marco Polo Bridge", in 1937/1939, again according to your source of information. This too, triggered a Japanese military response.
The Mukden Incident ~ see related link below .