In 1931, Japan had invaded and occupied Manchuria. Throughout the 1930s, China suffered continued territorial encroachment by the Japanese using their Manchurian base. Tensions continued to build as Japan gradually started to take over the whole north of the country. These tensions sparked at the Marco Polo Bridge Incident in 1937. Japanese troops were eventually driven away and the entire incident was considered only a minor skirmish at the time, but this battle served to mark the beginning of the Second Sino-Japanese War.