  We present a simple, self-consistent model to predict the maximum masses of
giant molecular clouds (GMCs), stellar clusters and high-redshift clumps as a
function of the galactic environment. Recent works have proposed that these
maximum masses are set by shearing motions and centrifugal forces, but we show
that this idea is inconsistent with the low masses observed across an important
range of local-Universe environments, such as low-surface density galaxies and
galaxy outskirts. Instead, we propose that feedback from young stars can
disrupt clouds before the global collapse of the shear-limited area is
completed. We develop a shear-feedback hybrid model that depends on three
observable quantities: the gas surface density, the epicylic frequency, and the
Toomre parameter. The model is tested in four galactic environments: the Milky
Way, the Local Group galaxy M31, the spiral galaxy M83, and the high-redshift
galaxy zC406690. We demonstrate that our model simultaneously reproduces the
observed maximum masses of GMCs, clumps and clusters in each of these
environments. We find that clouds and clusters in M31 and in the Milky Way are
feedback-limited beyond radii of 8.4 and 4 kpc, respectively, whereas the
masses in M83 and zC406690 are shear-limited at all radii. In zC406690, the
maximum cluster masses decrease further due to their inspiral by dynamical
friction. These results illustrate that the maximum masses change from being
shear-limited to being feedback-limited as galaxies become less gas-rich and
evolve towards low shear. This explains why high-redshift clumps are more
massive than GMCs in the Local Universe.
