  Semiconductor moir\'e superlattices have been shown to host a wide array of
interaction-driven ground states. However, twisted homobilayers have been
difficult to study in the limit of large moir\'e wavelength, where interactions
are most dominant. Here, we conduct local electronic compressibility
measurements of twisted bilayer WSe$_2$ (tWSe$_2$) at small twist angles. We
demonstrate multiple topological bands which host a series of Chern insulators
at zero magnetic field near a 'magic angle' around $1.23^\circ$. Using a
locally applied electric field, we induce a topological quantum phase
transition at one hole per moir\'e unit cell. Our work establishes the
topological phase diagram of a generalized Kane-Mele-Hubbard model in tWSe$_2$,
demonstrating a tunable platform for strongly correlated topological phases.
