This study examines the relationship during their formative periods between Hanbalism—which occupies a place within the Sunni tradition and has been increasingly recognized in recent research for its distinct theological dimension alongside its practical structure—and Ash'arism, which is accepted as having systematized the theological views of Shafi'ism, another school of the People of Hadith, into a form of systematic theology (kalam). This three-hundred-year period, spanning from the 9th to the 11th centuries, marks an era of significant evolution in philosophical and mystical thought, as well as one that was highly dynamic in political and social terms. While the work focuses on Baghdad and its surrounding areas, where the relationship between Hanbalism and Ash'arism was most intense, other cities to which these debates spread, such as Nishapur and Damascus, have not been overlooked; furthermore, the roles of regional states in the interaction between these schools have been highlighted. Today, there is an increase in studies that evaluate sectarian schools through the relationships they establish with their opponents or with one another. Inter-Sectarian Struggle aims to offer a new contribution to research in this field.