Asian monsoon rainfall impacts one third of the global population and predicting its variability and future change is of clear importance. However, the dynamics of even the climatological monsoon are not fully understood. Three independent subsystems are traditionally considered: the East Asian, South Asian, and Western North Pacific monsoons. Here we use idealized model simulations with east-west thermal contrast to explore the complex observed onset behavior of these subsystems. Our results suggest that the summertime ‘stationary wave’ monsoon circulation is not simply a passive response to insolation, but instead expands northwestwards and then eastwards via advective and evaporative feedbacks. In particular, our simulations indicate that onset over the Western North Pacific results from eastward extension of the summertime continental low via atmospheric feedbacks. We propose that the regional monsoons’ responses to forcings may be understood by considering how these feedbacks are influenced by the background state.