The first and northernmost of the four Crusader states, founded in 1098 when Baldwin of Boulogne, a leader of the First Crusade, was invited to rule the Armenian-populated city of Edessa on the upper Euphrates in northern Mesopotamia.
Reduced by piecemeal reconquest under the Artuqids and then Zengi of Mosul; the fall of the city of Edessa in 1144 (the event that triggered the Second Crusade) broke the county, and its last Frankish remnants were lost by c. 1150.
Not Edessa-specific alone, but the best focused study of Frankish rule over the mixed Armenian/Syriac Christian population of the County of Edessa and the northern crusader states generally; used here as the closest verified polity-relevant title after a specific Edessa monograph did not verify on Open Library.