In the space of less than two decades, Japan carved out a large empire in Indochina. In the process, they drove Western colonial powers such as the British, the French, and the Dutch out of territories that they had occupied for centuries.
Once they had established themselves in their newly-conquered territories, the Japanese proved extremely hard to remove and fought with a mixture of bravery and fanaticism right up until the end of World War II.
The desperation with which the Japanese fought to hold onto the lands they'd conquered was in some measure related to the essentially ideological motivation behind the building of their empire. Right-wing nationalism became a powerful force in Japanese politics in the 1930s and dictated the policy of imperialism that would be followed from then until 1945.
According to nationalist ideology, the Japanese were racially superior to the so-called lesser races of Indochina. In their minds, this gave them the right to conquer their alleged racial inferiors as part of their grand imperialist designs.
When the Japanese conquered lands in this part of the world, they put their nationalist ideas into practice by treating local populations with unimaginable barbarism. Yet as far as the Japanese conquerors were concerned, they had the perfect right to do this on account of their racial superiority.
The Japanese weren't simply motivated to build their Indochinese empire by nationalism and notions of racial superiority. Japan was chronically short of raw materials such as oil, timber, and rubber, and so it was considered necessary by the Japanese military and political elite to take what was needed by force from neighboring countries.
In establishing their empire, the Japanese also looked to be able to compete with the Western powers on the international stage. They wanted Japan to be a major power engaged in geopolitical rivalry with the likes of the Soviet Union and the United States. This desire emanated from the fanatical nationalism and racism that we examined earlier. The Japanese believed themselves to be a breed apart, a special race that was fully entitled to a place in the sun along with the other great international powers.