Why have nation-states been more successful, as political units, in modern world history then multinational empires have been?

the mexican-american war was a conflict between the united states and mexico, fought from april 1846 to february 1848.

lancelot said to the beautiful ellen i c u r a b u t l n (i see you are a beauty lancelot was the greatest and worst of the knights who became the king's champion and undertook quests in the king's name. he became the adulterous lover of queen guinevere, and they had a son named galahad.