Succession and rule in mediaeval Europe was not as cut and dried as it might seem when you read neat family trees showing elder sons succeeding their fathers. Infant mortality was such that it was quite common for a succession of children to die before reaching adulthood. And many an adult king was cut down in the prime of life by an injury or disease that wouldn’t even require hospitalisation these days.
So the history of any European country is full of regents; of uncles and powerful nobles with vaguely appropriate bloodlines stepping in to run the country when the opportunity presented itself. And often the one wielding the power was a woman; generally speaking in the name of a young son, or running the country while her husband or son was off fighting wars somewhere else.
But very occasionally, a woman managed to wield the power in her own name. Melisende, Queen of Jerusalem was one of those.
Melisende was Frankish, although she spent her entire life in the Middle East. She grew up in Edessa, until her father Baldwin II became King of Jerusalem when she was 13. Jerusalem had been conquered by the Crusaders only 19 years before, after the first Crusade. She was the oldest daughter in a family of daughters, with her father refusing to divorce Melisande’s mother, Morphia, even though he really needed a son to cement his family’s hold on the Kingship. Instead, he raised Melisande as his successor, naming her Crown Princess, and gradually giving her increasing power. Her name was included with her father’s on many official documents, and she was supported by the ruling council.
But, of course, being female, she needed a husband to give her added credibility. It was very difficult to find the most appropriately prestigious person. Too prestigious and powerful in his own right, and he would take over, freezing her out. Not prestigious enough, and her own credibility would be diminished by a poor marriage choice. Baldwin and Melisende erred on the side of power, and chose Fulk V, who was Count of Anjou, and one of the most powerful nobles in France, after the King himself. They took steps to keep the power for Melisende, crowning her Queen jointly with her father, once she had given birth to a son, also called Baldwin, (presumably proving her dynastically worth of the title).
But once Melisende’s father Baldwin died in 1131, Fulk did exactly as expected, and increasingly froze Melisende out of power until four years later, he accused her of adultery, with her cousin, Hugh, and used that as an excuse to take over the reigns of power from her. But when Fulk exiled Hugh, and attempted to assassinate him, Melisende fought back, and managed to freeze Fulk out of power, pulling in support from the nobles around court and taking back the reigns of power in 1135, and once again signing all the relevant court documents, and generally acting as Queen of the land.
Eventually she did pass power to her son, Baldwin III. But not without a fight. She showed no signs of passing on power so eventually he started protesting in the streets. When the noble council considered the matter, they split the kingdom up, giving Melisende the lion’s share, including Jerusalem. Baldwin III wasn’t happy about that, (although he got Acre, at the time the key port in that part of the Mediterranean) so he almost immediately declared war. The Church was called in to mediate, and power was largely passed to Baldwin, but with Melisende frequently acting for him whenever he was off on military campaigns.
In the end, Melisande was undisputed ruler of Jerusalem for around 20 years, which was a long time in such a tumultuous period and, particularly in that part of the world. The territory owned by the Jerusalem Kingdom waxed and waned during her tenure – the southern borders with Egypt were strengthened, but the second Crusade completely failed to take Damascus in 1148, which meant that the support from Europe diminished substantially in the next few decades. Overall it seems as if she managed the kingdom as well as any other Christian ruler of the hundred years they had Jerusalem.