The most intense star formation in the universe takes place in dusty, star-forming galaxies at high redshift. Recent observations and circumstantial evidence suggest that these galaxies are the likely progenitors of the earliest generation of massive, quiescent galaxies. I will discuss recent efforts to detect and resolve the gas and dust on sub-kiloparsec scales using observations of gravitationally lensed dusty galaxies discovered by the South Pole Telescope conducted by ALMA and other facilities. These observations demonstrate the richness of the molecular ISM, shed light on the relative distribution of star formation and the gas from which stars form, and offer a unique window into the evolution of dusty galaxies impossible to obtain without the aid of gravitational lensing. Finally, I will present new ALMA observations which show signs of feedback on the molecular ISM in dusty star-forming galaxies, providing tantalizing evidence of an evolutionary connection between high-redshift dusty galaxies and the first massive, quiescent systems.