Construction of an L_*—Galaxy: the Transformative Power of Wide Fields for Revealing the Past, Present and Future of the Great Andromeda System

Our understanding of the M31 system will be transformed in the 2020s with wide field facilities for photometry (HST-like sensitivity and resolution) and spectroscopy (10 m class telescope, > 1 deg2 field, highly multiplexed, R ~ 3000 — 6000). We focus on the power of these facilities to constrain the past, present, and future merger history of M31.