  During star cluster formation, ongoing mass accretion is resisted by stellar
feedback in the form of protostellar outflows from the low-mass stars and
photo-ionization and radiation pressure feedback from the massive stars. We
model the evolution of cluster-forming regions during a phase in which both
accretion and feedback are present, and use these models to investigate how
star cluster formation might terminate. Protostellar outflows are the strongest
form of feedback in low-mass regions, but these cannot stop cluster formation
if matter continues to flow in. In more massive clusters, radiation pressure
and photo-ionization rapidly clear the cluster-forming gas when its column
density is too small. We assess the rates of dynamical mass ejection and of
evaporation, while accounting for the important effect of dust opacity on
photo-ionization. Our models are consistent with the census of protostellar
outflows in NGC 1333 and Serpens South, and with the dust temperatures observed
in regions of massive star formation. Comparing observations of massive
cluster-forming regions against our model parameter space, and against our
expectations for accretion-driven evolution, we infer that massive-star
feedback is a likely cause of gas disruption in regions with velocity
dispersions less than a few kilometers per second, but that more massive and
more turbulent regions are too strongly bound for stellar feedback to be
disruptive.
