Historians often characterize Japan's foreign policy regarding China during the 1920s as dominated by economic priorities and a commitment to peaceful cooperation within a collaborative system of treaty port imperialism. In that narrative, the Manchurian Incident of 1931 thus stands as a watershed moment in modern East Asian history when Japan returned to a policy of acquiring formal colonial territory. Akira Iriye made this thesis famous with his groundbreaking international history of East Asia during the 1920s. More recently, Peter Duus has reinforced this paradigm in his summary of Japan's informal empire, pondering why it was that ‘just when Japan appeared to be emerging as the paramount foreign economic power in China within the framework of the treaty system, it embarked on a new policy of establishing direct political control over Manchuria’ in the autumn of 1931. Similarly, Mark Peattie has also suggested that ‘in the overheated atmosphere of the 1930s, the Japanese empire once more became expansive,’ clearly emphasizing the notion that a return to previously abandoned patterns of colonial conquest was underway.