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Serbia had not been a country for over 300 years at the time of the American Revolution. After some uprisings in the early 19th Century, the Ottomans gave the Serbs a degree of autonomy, but Serbia did not gain full and internationally recognized independence until the Congress of Berlin in 1878(?). USA-Serbian diplomatic recognition and relations date from shortly after that time. You were off by about 100 years, but no problem, in Balkans-time that's like yesterday.
since you want to go into history: who was there first, the albanians or the serbs?
I rest my case.
when was Serbia first a nation?