I recently answered another question here about how people became pirates in the early 18th century which answers a lot of this question. Like the answer to that question, what kinds of people became pirates could vary hugely. The majority of pirates were poor sailors, from lower class backgrounds just like the majority of regular non-piratical sailors at the time. Some were habitual criminals from the very lowest dregs of society, like Edward Low. There were also a few that came from wealthier backgrounds or who had been officers aboard ships before becoming pirates, like Edward Thache (Blackbeard) and Bartholomew Roberts. More than a few pirate captains fit into the latter category, and that probably has something to do with them being better educated and therefore standing out and being able to take control. One pirate captain, Stede Bonnet, who is probably one of the most unusual pirates of all, had actually been a wealthy plantation owner before he recklessly decided to outfit a ship at his own expense in 1717 and begin engaging in piracy.

The vast majority of pirates in the early 18th century were English speaking and either from the British isles or born in the American colonies with recent British ancestors. Within Britain, most were English and many of those were from the West Country in southwestern England from places like Bristol which had a long maritime history and were where a lot of sailors were from. A surprising number of famous pirates were Welsh, like Bartholomew Roberts, Howell Davis (and Henry Morgan in the 17th century). Others like William Kidd and John Gow were Scottish, and there were a few Irish pirates like Walter Kennedy and Anne Bonny. There were some French pirates like Olivier Levasseur (called La Buse) and especially in earlier times, in the 17th century, a significant number of buccaneers were French but there were also Dutch buccaneers and a few Spanish ones. There are some very limited indications that there might have been a few African pirates who were freed slaves, but it's very unclear if this was ever actually the case (Leigh). At least in the 17th century there were also a few Native Americans from the Mosquito Coast in modern Nicuragua and Honduras who joined the buccaneers (Exquemelin, Dampier). A typical pirate crew would have tended to be overwhelmingly composed of one nationality or at least language group.

Not only does this question vary hugely in the specific timeframe of the early 18th century, however, but also throughout the heyday of piracy beginning almost a century earlier. In the 17th century, things were somewhat different than what I've described. The range of your question from 1400-1900 is hugely broad and couldn't possibly be covered in one comment or book, so that's why I'm confining it to the so-called "Golden Age of Piracy" in the early 18th century. If you have any other questions I can try to answer them.

Sources:

Under the Black Flag by David Cordingly

The Historical Record of Black Caesar by Devin Leigh

The Buccaneers of America by Alexandre Exquemelin

A New Voyage Round the World by William Dampier

A General History of the Robberies and Murders of the Most Notorious Pyrates by Charles Johnson