How did composers express musical nationalism in their music?

Strong tunes, often marching music with drums. Also, they could add nationalistic lyrics to their music. Describing the country, it's structure or it's people. The feelings and dreams they have. The rules they abide to.

The answer is

The gregorian chant was a major cultural milestone in the middle ages. it was one of the first codified forms of music meant to be played as written, where previously it was difficult to mass-produce and disseminate any music. what's more, these chants were also some of the first examples of musical notation: the notes and bars of today's music sheets are a reflection of centuries of evolution beginning with these chants. it became official throughout the entirety of the catholic church, meaning that nearly all of europe followed this musical notation and styling.