How did nationalism threaten the existing political order of the nineteenth century? message me : )

Answers;
Nationalism was a threat to the existing order in the nineteenth century in Europe; Because many monarchies at the time combined people of many nationalities who wanted their own governments.

Explanation;
Beginning in the 19th century, the elites started indoctrinating populations in new national identities.
These identities provided the material for nationalist appeals for sacrifice during wartime and preparation for war during the peaceful periods between wars.

During the 19th century, nationalism led many countries in Europe to gain a feeling of superiority over other countries, which led to large-scale war and invasions, eventually leading to WWI.