"I come from China."
Translation:Vengo dalla Cina.
No, I think the only preposition that wouldn't be followed by the article before a nation is "in"; "sono nato in Cina" (I was born in China).
"Vengo da Cina" was marked as incorrect. Is it compulsory to use definite article before the name of a country.
Hm, no sorry; on wordreference's forum they mention an online map but the link isn't working anymore. It's rather hard to derive a list too; in the case of countries the exceptions are usually either city-states or island-states (e.g. Malta or Cuba), but that isn't a general rule either...