We consider a sequential merger game between Cournot firms with homogeneous product and quadratic cost function. A large slope of the marginal cost function or a small slope of inversemarket demand are both predicted to increase the incentive to merge. The profitability of any merger is predicted to increase with the number of mergers having already taken place. Thus, mergers tend to occur in waves in industries that have experienced exogenous shocks affecting firms’ cost or demand. We also show some mergers that are not profitable for merged firms in the short-run may take place in the early stage of a wave. The model helps reconcile some of the most important stylized facts about merger and acquisition activities over the last century.