Although the Kwantung Army was nominally subordinate to the Imperial General Headquarters and the senior staff at the Army General Staff located in Tokyo, its leadership often acted in direct violation of the orders from mainland Japan without suffering any consequence. Conspirators within the junior officer corps of the Kwantung Army plotted and carried out the assassination of Manchurian warlord Zhang Zuolin in the Huanggutun Incident of 1928. Afterward, the Kwantung Army leadership engineered the Mukden Incident and the subsequent invasion of Manchuria in 1931, in a massive act of insubordination ("gekokujo") against the express orders of the political and military leadership based in Tokyo.