I study the history and dynamics of the Milky Way galaxy, using old stars, dwarf galaxies, and globular clusters in the Galactic halo. Information from these structures provides clues towards understanding the distribution and nature of dark matter, the absence of Pop III stars, and the dynamics of dwarf galaxy disruption. I have recently helped in mapping the density distribution of the Sagittarius dwarf galaxy's tidal debris tails, which imply an orbit around the Galaxy, and serve as tracers for the distribution of mass (including dark matter) in the Milky Way. These studies use data from the Sloan Digital Sky Survey (SDSS), the Two Micron All Sky Survey (2MASS), and the Chinese Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST).