The standard genesis narrative of the modern Middle East is largely uncontested: with the fall of the Ottoman Empire at the end of World War I, the British and French imposed artificial borders on the region in the postwar settlement. In the Treaty of Sèvres and subsequent “oversight” of the mandates awarded these two Great Powers, the League of Nations legitimated this neo-colonial reorganization of the post-Ottoman Middle East. The standard narrative focuses almost exclusively on the partitioning of greater Syria and unification of Iraq (with little attention to Anatolia or the Arabian Peninsula and none to Northern Africa). It also focuses almost exclusively on the causal agency of the British and French in introducing and delineating territorialized political units that contravened the aspirations of the local population, a legacy that constitutes the “original sin” at the root of present-day conflicts. This paper challenges this explanation by historicizing the actual processes through which territorialized state space was produced and eventually delineated during a post-1918 long decade extending into the 1930s. Moving beyond the mandates (Iraq, Syria, Palestine), I consider a wider transregional scope that extends from Northern Morocco to the Iranian plateau. In this post-Ottoman greater Middle East, I argue that—rather than being unilaterally imposed by European powers—state-based territorialization was actually driven by anti-colonial warfare waged across the region in the decade following Paris Peace Conference by local challengers seeking to realize their own political visions. This analysis draws on multi-country archival research (including Spanish, Italian, French, and British military and administrative records, and Arabic correspondence and periodicals) to trace how a series of revolts in the mid- to late-1920s—the Rif War in Northern Morocco, the Italo-Sanusi war in Libya, the Great Syrian Revolt, the Shaykh Said and Ararat Kurdish revolts, and the Saudi-Ikhwan expansion in the Arabian Peninsula—forced nascent colonial states (and the Turkish Republic) to both define and enforce territorial boundaries within a still highly fluid postwar political space. This alternative narrative better accounts for how, why, and when the Middle East’s modern political borders were defined. They were not imposed unilaterally but negotiated and produced through violent and complex interactions involving both colonial and local forces.