Although the Manchurian Incident in 1931 launched the Fifteen-Year War and Japan's major push for territorial expansion, even before this drive began, Japan had colonized Korea, Taiwan and southern Sakhalin, taken control of the Chinese state of Guangdong through a leasehold agreement, and begun governing numerous islands in the South Pacific under League of Nations mandates. When the War broke out, many people from these occupied countries and territories were mobilized to work in the munitions industry, sometimes even being brought to Japan against their will to work for Japanese companies. Many were drafted as soldiers, while others were mobilized as civilian support for Japanese troops.

Local governments in occupied China and Southeast Asian were replaced with puppet regimes through which the Japanese army could exert control and force cooperation with Japan in the War. People in the occupied territories were also forced to assimilate to Japanese culture and show respect for the Japanese Emperor.

Many of the people in the Asian territories occupied by Japan actively resisted Japan's aggression and occupational rule. Japan, in turn, made excuses for its actions and tried to find people who would cooperate with the occupying forces, but it failed to win the hearts and minds of the local populations. When people refused to cooperate, Japanese troops used brute force to suppress resistance, destroying cities and villages where they encountered trouble. Even so, resistance did not die out. The anti-Japanese activities of the Asians under Japanese control were eventually tied into international movements against war and Fascism, and ultimately, formed the basis of national independence movements.