score:12
Japan did not conquer Vietnam, it had already been conquered by the French. For most of the war Japan left the existing French colonial government in place and negotiated the rights to station troops there and move them through the country.
Initially, Japan was only interested in Northern Indochina to cut off supplies to China. To this end they signed an accord with Vichy France in Sept 1940 to be able to station and move a limited number of troops through French Indochina (modern Laos, Cambodia, and Vietnam). The Japanese immediately violated this but eventually things settled down. Japan did not advance further south for fear of antagonizing the US and Britain.
In October 1940 Thailand took the opportunity of France's weakness to win back territory lost in the Franco-Siamese War of 1893. After defeats for the French, the Japanese stepped in to mediate a cease-fire in January 1941. France ceded disputed border provinces to Thailand.
Realizing they could no longer defend their overseas territories, and not being at war with Japan, in July 1941 Vichy France signed the "Protocol Concerning Joint Defense and Joint Military Cooperation". This secured Indochina for the Vichy French and gave the Japanese airfields and bases close to attack South East Asia.
This state of affairs of mostly peaceful cooperation between the French colonial government and Japanese military continued until almost the end of the war. In March 1945, with France restored and the war turning against them, the Japanese launched a coup d'Γ©tat in Indochina. They redeployed their troops to surround the French garrisons and suddenly ordered them to disarm. Fighting was brief, and in a single day the Japanese dismantled French rule in Indochina.
The Japanese split Indochina into three puppet states under sympathetic rulers: the Empire of Vietnam, the Kingdom of Kampuchea (Cambodia), and the Kingdom of Laos and made them all part of the Greater East Asia Co-Prosperity Sphere.
By handing Vietnam independence from French colonial rule, and eventually allowing reunification of north and south Vietnam, Japan avoided a fight with the native populations. Once the Empire of Japan fell, the short lived Empire of Vietnam did as well and the Viet-Minh took over in the August Revolution.
Upvote:-4
Japan was only occupying small areas that had economic importance, not trying to control the whole country.
Also, in world wars soldiers do not guff around. If civilians misbehave, they will just go in and machine gun everybody. When the U.S. was in Viet Nam, we put all sorts of political restrictions on the soldiers, such as not allowing them to shoot civilians. The Japanese were under no such restrictions and in all the areas they occupied they brutally slaughtered anyone involved in resisting them. For example, after the Doolittle Raid, the Japanese completely wiped out the Chinese villages that had sheltered the American pilots. They murdered everyone, some 20,000 people or more, man woman and child, and burned down every single building in an 80-mile radius. They even killed all the livestock; every single cow, goat, chicken, dog, whatever. With policies like that, the civilian resistance to the Japanese occupation was pretty limited.
Upvote:6
The Japanese conquered Singapore a much more visible, if smaller target with some 35,000 men (far fewer than the defenders). They also conquered the Philippines with a force of about 130,000 men, against mixed American-Filipino forces.
That was because of two reasons. 1) the Japanese troops were better at jungle fighting than the French, British and Americans. 2) With a war going on in Europe neither Vichy France (the occupied by Nazi Germany with a 90,000 man size limitation on her army), nor Britain could spare meaningful forces for the Far East. America was also unprepared for war. In that context, the 140,000 man army that the Japanese committed to Vietnam was enormous. Chinese proverb: "When no tiger is on the mountain, the jackal is king."
The Vietnamese were not armed or trained for fighting until after World War II. The war did a lot to "educate" them in this regard. Put another way, Japan was "in the right place at the right time." In the words of U.S. Civil War cavalry general Nathan Bedford Forrest, they "got there firstest with the mostest."