This article addresses why the campaign of Kerbogha’s combined forces against the First Crusade failed by using accounts in Arabic, Armenian, Greek, Latin, and Old French. The discussion starts with an overview of how the different claims that explain the campaign’s failure have evolved since the eighteenth century. Then, for the first time, Kerbogha’s route from Mosul to Antioch has been precisely recreated, revealing a longer campaign than formerly estimated. The focus of the article then discusses the reasons why Kerbogha besieged Edessa. This section is followed by an explanation of why the failure of the siege led to the collapse of the entire campaign. Finally, the tactics used during the battle of 28 June 1098 are re-evaluated by considering the poor condition of the combined Muslim force. The article claims the campaign primarily failed because of the deficient structure of the army and the rivalries between its commanders.