Fun Fact: Pirates! is the first Sid Meier game to use his name in the title for marketing purposes
The NES version of Pirates! was a port from the original Commodore 64 version. Players chose one of six eras that spanned the 16th and 17th centuries, which would determine current events and some affect the difficulty. Choice of nationality could make the game easier or harder depending on whether the government in question supported piracy. After a choice of special skill and difficulty level the player was off to sail the seven seas and kill people and pillage and all the other things that pirates never actually seem to do all that much in the Disney movies.
There isn't a whole lot to differentiate this port from other ports of the original, but NES players who enjoyed strategy were glad to have this option available.