jats:titleAbstract</jats:title>jats:pThe transition of a passive continental margin into a subduction zone remains a hypothesis because few geological cases have been reported. The North Sulawesi subduction zone is a 5–9 myr system in Southeast Asia that has evolved from a passive continental margin and has long been overlooked by studies of passive to active margin transitions. Here we compare geophysical evidence from the region with our numerical simulation results. We find that the initial subduction of North Sulawesi relies on horizontal stress, where the trench retreat depends on the negative buoyancy of the oceanic lithosphere. Furthermore, less space available for subduction leads to reduced mantle flow caused by subduction and slower trench retreat. These new dynamical constraints indicate that the negative buoyancy of the oceanic plate is a key factor for the trench retreat, even though subduction initiated was induced.</jats:p>