Thanks to the Gaia mission, we can now identify candidates for dwarf galaxies that the Milky Way has accreted and disrupted. In this talk, I will discuss how we can characterize these building blocks of the Milky Way through high-resolution spectroscopy of the member stars. By achieving high precision in the measured chemical abundance, we reveal distinct differences in abundance ratios among them. These differences largely stem from varying contributions by type Ia supernovae in their chemical enrichments. Additionally, I will demonstrate that deriving accurate abundances through 3D non-LTE analysis is critical for the clear chemical separation of certain stellar populations in the Milky Way halo. Our findings highlight the importance of both precision and accuracy in chemical abundance measurements for the detailed chemical characterization of the Milky Way's stellar populations.