  We introduce a stochastic model in which adjacent planar regions $A, B$ merge
stochastically at some rate $\lambda(A,B)$, and observe analogies with the
well-studied topics of mean-field coagulation and of bond percolation. Do
infinite regions appear in finite time? We give a simple condition on $\lambda$
for this {\em hegemony} property to hold, and another simple condition for it
to not hold, but there is a large gap between these conditions, which includes
the case $\lambda(A,B) \equiv 1$. For this case, a non-rigorous analytic
argument and simulations suggest hegemony.
