  We use simulations with realistic models for stellar feedback to study galaxy
mergers. These high resolution (1 pc) simulations follow formation and
destruction of individual GMCs and star clusters. The final starburst is
dominated by in situ star formation, fueled by gas which flows inwards due to
global torques. The resulting high gas density results in rapid star formation.
The gas is self gravitating, and forms massive (~10^10 M_sun) GMCs and
subsequent super-starclusters (masses up to 10^8 M_sun). However, in contrast
to some recent simulations, the bulk of new stars which eventually form the
central bulge are not born in superclusters which then sink to the center of
the galaxy, because feedback efficiently disperses GMCs after they turn several
percent of their mass into stars. Most of the mass that reaches the nucleus
does so in the form of gas. The Kennicutt-Schmidt law emerges naturally as a
consequence of feedback balancing gravitational collapse, independent of the
small-scale star formation microphysics. The same mechanisms that drive this
relation in isolated galaxies, in particular radiation pressure from IR
photons, extend over seven decades in SFR to regulate star formation in the
most extreme starbursts (densities >10^4 M_sun/pc^2). Feedback also drives
super-winds with large mass loss rates; but a significant fraction of the wind
material falls back onto the disks at later times, leading to higher
post-starburst SFRs in the presence of stellar feedback. Strong AGN feedback is
required to explain sharp cutoffs in star formation rate. We compare the
predicted relic structure, mass profile, morphology, and efficiency of disk
survival to simulations which do not explicitly resolve GMCs or feedback.
Global galaxy properties are similar, but sub-galactic properties and star
formation rates can differ significantly.
