Despite immense success in describing the universe on large scales, the LCDM model faces several outstanding small-scale conflicts between observations of dwarf galaxies in the Local Group and the low-mass dark matter halos expected to host them. Alternative dark matter models, such as sterile neutrinos and ultralight axions, possibly resolve the small-scale tensions found in CDM by suppressing structure formation on sub-galactic scales. I will present high-resolution N-body simulations of the Local Group that we are using to explore how various DM models affect the growth of structure on small scales from high redshifts to the local Universe. I will also show how high-redshift galaxy counts, reionization measurements, and the Lyman-alpha forest can be used to constrain these alternative DM models. Lastly, I will discuss simulations of tidal streams that probe the Milky Way’s potential with the aim to identify the predicted “dark” subhalos of CDM.