The hierarchical nature of galaxy formation in the standard model of cosmology (LCDM) predicts a diffuse stellar halo component around Milky Way-mass galaxies, formed from the accretion and disruption of dwarf galaxies. Using cosmological hydrodynamical simulations, I will discuss the radial build up of stellar halos from the accreted dwarfs and will connect these results with recent findings from the Gaia mission related to the major event in the formation history of the Milky Way (Gaia-Enceladus-Sausage). I will discuss whether this event is unusual and whether it has any implications for dark matter distribution and dark matter direct detection experiments.