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.

though both had similar roots, they both took these similar bases & formed it into their own way. both the byzantine empire and ancient roman have similar aspects, but each one made it unique. both the byzantine empire and ancient romans had roman influences which affected their culture