With computer simulations, we study the interplay between thermo-mechanical processes in the lithosphere and the underlying upper mantle during a long-term (> 100 Myr) tectonic cycle of extension–cooling–convergence. The intensity of mantle convection is important for (i) subduction initiation, (ii) the development of single- or double-slab subduction zones, and (iii) the forces necessary to initiate subduction. Our models are applicable to the opening and closure of the western Alpine Tethys.