  We model the formation of high-mass stars, specifying the accretion rate in
terms of the instantaneous and final mass of the star, the ambient pressure of
the star-forming region and the form of polytropic pressure support of the
pre-stellar gas core. The high pressures typical of Galactic regions of massive
star formation allow a 100 solar mass star to form in ~10^5 years with a final
accretion rate ~10^-3 solar masses per year. By modeling protostellar evolution
we predict the properties of several nearby massive protostars. We model
cluster formation by applying this theory to many stars. We use the observed
intensity of outflows from protoclusters to estimate the star formation rate,
finding that clusters take at least several free-fall times to form; for a
cluster similar to the Orion Nebula Cluster, we predict a formation timescale
of ~1x10^6 years.
