Yo Ho, All Hands The open ocean is a battleground. The British government is fully at war with multiple factions of pirates at one time. Due to their guerilla tactics, occult knowledge, and in large part their cunning the pirates have put up quite a fight against the greatest Navy the world has ever known. This is even with the help of the highly skilled witch hunters known as Bishops, whom answer directly to the queen. All ordained by the Church of England, each experienced exorcists and witch hunters in their own right. Now they are a unified front guiding the British Navy in eradicating the forces of Satan which have taken refuse under the floating flag of piracy.
Anyone foolish enough to listen to barroom rumors may believe pirates fight for freedom, or something as outlandish as democracy. However, the stories of the atrocities they commit at sea should be plenty to discourage any young man or woman from seeking out a recruiter from the shadows. If that weren't enough, the loss of one's immortal soul should dissuade thee, no? If you still believe there's a life outside of the king's rule, then so be it. You'll have to swear allegiance to a pirate lord, and you likely won't have your pick. They'll snatch you up into their war, or leave you trailing behind the boat as bait for sharks to feed their fleets with.
Hoist the Colors High
The Sea Witch Veronica Boudreaux commands a true loyal cult of a crew. They are the most fitting the description of devil worshipers, though their only goddess is Veronica herself. Members of her fleet carve runes into their skin, take part in ritual sacrifices (usually using captured enemies, but occasionally themselves) and are known to be the most bloodthirsty during raids. To see their black flag waiving a pentagram is to accept one's death, it's said. This reputations is only made worse by the fact that the British Navy has yet to best them in a large scale engagement. Twice they've suffered severe losses and given up ground in the Caribbean thanks to Veronica's devotees.
Yet, occasionally you will hear the British sink a line ship or fend off a raiding party. Every time, Veronica's sailors die to the last man. Some runes seem to induce suicide on command, even when one is captured alive. What dark secrets could possibly be worth protecting that closely?
Heave, Ho, Thieves, and Beggars
William Kidd is the leader of the Republic of Pirates whom have their base in Nassau. These vagabonds and miscreants are the closest to the ideals that the pirates so often preach. Though they have their fair share of squabbles between them, they have managed to keep their band together despite regular defeats from the British. Their arcane power is nothing compared to the Sea Witch's cult, but Kidd Himself is said to have powers of foresight that even surpass Veronica's. Perhaps this is why when the Republic and the Sea Cult have clashed, the Republic has muddled through with few losses. All in all they may only be a thorn in the side of the British Government who's good at making money via crime, but they remain the Navy's number two targets nonetheless. Perhaps because if they stand a chance at wiping anyone out in a timely manner, it's the plucky little Republic.
Though it is only the second most profitable of the three pirate nations, most common folk looking to start a life of piracy come to one of their fleets. That is, the fleets of Anne Bonny, "Calico," Jack Rackham, or William Kidd himself. "The Three Dukes," they're called, and they offer the most honest deal. Any crew member may quit at any time without fear of repercussions. Each man gets one share of any loot gained, save for the quartermaster, doctor, and Captain who all get 1.5 shares. This means a sailor has the best chance to make a living under the Republic, and get out alive.
Never Shall We Die 
Then, of course, there's Blackbeard himself. The only Pirate Lord who has an unbroken winning streak against the Empire. After the first three engagements with the navy, Blackbeard spent huge portions of gold on buying out the most talented battle mages in Europe. The most destructive elemental mages, the deadliest necromancers (not already employed by Veronica, of course), and then he spent the rest of his coffers on the toughest sell swords from any nation. Fencers, descendants of knightly houses, eastern swordsmen, and even assassins line his decks. If any of the pirate nations can truly be called a Navy in it's own right, it is Blackbeard's fleet. Now that he has this winning streak going, he's more than made his money back on that investment. One would expect the most brutal and money hungry of all pirates to have something big planned on the horizon.