The first Crusade, a massive and unprecedented undertaking in the western world, differed from the majority of subsequent crusades into the Holy Land in an important way: it contained no royalty and was undertaken with very little direct support from the ruling families of Western Europe. This aspect of the crusade led to the development of sophisticated hierarchies and vassalages among the knights who led the crusade. These relationships culminated in the formation of the Crusader States, Latin outposts in the Levant surrounded by Muslim states, and populated primarily by non-Catholic or non-Christian peoples. Despite the difficulties engendered by this situation, the Crusader States managed to maintain control over the Holy Land for much of the twelfth century, and, to a lesser degree, for several decades after the Fall of Jerusalem in 1187 to Saladin.
Osterhaug, Tobias, "A Political History of the Kingdom of Jerusalem 1099 to 1187 C.E." (2014). WWU Honors Program Senior Projects. 25.