The question of how the Pirate Lords of Avalon ... dear me, that IS a title waiting to happen - established themselves as buzzard kings of the Hesperian is another interesting one; more interesting still is the question of how Atlanteans reacted to the Wars of the Three Kingdoms (of which the English Civil War is the most famous part of that bloody cycle), which strikes me as something of a missed opportunity.
If nothing else, the breach between King & Parliament makes an excellent stressor driving an Atlantean desire to walk away from the whole sorry mess as an independent nation in its own right - and one can only wonder how a War of Independence fought with the weapons & tactics of the 17th Century would have differed from the American Revolutionary War fought a century later.
In all honesty, one can only suspect that either the cavaliers or the roundheads put some nasty lads with quick ships and hasty tempers into Avalon for the sake of harassing their rivals, who then proceeded to make themselves useful enough against the Dutch (and for all we know the French & the Spanish too) once the Civil Wars were done to allow them to escape the consequences of their privateering 'mischief' ... right up until the moment peace broke out, a new generation of pirates kept up some old bad habits and suffered the consequences when some cold, considerate men decided the days of Roaring Boys were DONE, their usefulness all used up.
Oh, and I'm fairly certain there must have been some interesting goings-on back in the days when Spain was The Power in the New World; I wonder if the Dons made a serious effort to oust the English & French from Atlantis? (or at least sought to use the English colonist's lingering loyalties to Rome to win them away from their Mother Countries).