Saqaliba

You've been kidnapped from your fishing village by pirate raiders, sold into slavery, castrated, and forced to work in the court of the Caliph.  One day, the country starts falling apart around you.  What do you do? This is the situation that faced the court slaves, or saqaliba, of Cordoba in 1010 AD.

For years, the Caliph had been reduced to a powerless figurehead while his viziers ruled the empire, but the pathetic tenure of Caliph Hisham II took the situation to a new level.  He (nominally) took the throne at age 10, dressed himself in a veil and makeup, and kept an all-male harem.  As one could imagine, this set of traits did not make for an imposing supreme ruler in eleventh century Iberia.  The actual power was all in the hands of his chancellor and general, Al-Mansur, who wouldn't even let Hisham leave his palace.

Al-Mansur was quite happy to keep the weird gay shut-in on the throne, but when he died his sons Abd al-Malik and Abd ur-Rahman didn't realize what a good thing he had going.  They wanted the title as well as the power, because what's the point in running a massive empire if you can't tell the ladies that you're Caliph?  After a series of uprisings, assassinations and other various and sundry court intrigue, they brought the Caliphate crashing down around them.

This put the saqaliba, Slavs who had been captured in raids or in battle, and brought to court to serve as eunuch slaves and advisers, in a tricky position.  Should they try to make it back to their homeland?  Keep their heads down and hope no one thinks they look like ripe assassination targets?  Those would probably be the sensible answers, but Mujahid al-Siqlabi (they apparently got spiffy new Arabic names in exchange for having their junk chopped off) had a better answer: get yourself a make-shift crown and a map, draw yourself a nice looking swath of territory and proclaim yourself a newly-minted petty king.  Then start duking it out with the other slaves who'd done the same thing.

Mujahid's Taifa of Denia somehow managed to get control of a nice patch of land along the Eastern coast of Spain, while other former slaves, generals and court dignitaries carved up the rest of Muslim Iberia among themselves.  This provided a lot of work for map-makers as the various kingdoms routinely attacked and absorbed one another until the Almoravids from Morocco arrived a few decades later to gobble the whole mess up.

The Republic of Bou Regreg

This sounds like something out of history mad-libs: In 1627, a Dutch convert to Islam lead a group of Moroccan pirates from his personal city state to the shores of Iceland to seek plunder and slaves.

The man in question is Jan Janszoon.  He started his career as a privateer, authorized by the Dutch crown to attack Spanish shipping.  After being captured by North African pirates in 1618, he converted to Islam (possibly at gunpoint, or possibly because the pirate crew made some very insightful theological arguments) and joined their crew.  After his captain was killed in battle the next year, he took control of the city of Salé on the Moroccan coast.  Although nominally under the control of the Sultan of Morocco, the city was essentially a self-governing pirate lair.  Jan (by then called Murat Reis) was elected their Grand Admiral, a position more commonly known as "Pirate King".  

Using the Republic of Salé (also known as the Republic of Bou Regreg, a way better name) as his base of operations, he raided the shipping throughout the Mediterranean, as well as up the Atlantic Coast to England and Ireland.   In 1627, he took a captured Danish sailor as his guide to Iceland, where he and his band of Moroccan pirates came upon the peaceful fishing village of Grindavík.  As it turns out, peaceful Icelandic fishing villages are not rich with plunder, so the pirates decided to abscond with a few local families instead.  

The Icelanders were sold into slavery back in North Africa, but a few of them were eventually rescued and returned to Iceland.  For his part, Jan was eventually captured by the Knights of Malta, and imprisoned and tortured in their dungeons for five years.  After his rescue by Tunisian corsairs, he returned to Morocco to a hero's welcome, and was granted governorship of a lavish fortress.