Nationalism led to major conflicts following world war , especially when

When a colonial power or a country that has a lot of ethnicities has lost a war, (it doesn't always have to be losing a war, the major power could just be heavily weakened and still won) especially a world war, many secession movements and rebellion movements will occur. This occured in the British and French empires. The African and Asian colonies started independence movements and rebellion.

A notable independence movement is Britain's India(British Raj).

A notable rebellion is Vietnam(French Indochina), in the First Indochina war.

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