An oligopolistic theory of regional trade agreements

Why are trade agreements regional? I address this question in a model of oligopoly featuring product variety. Tariffs have the effect of manipulating a country's terms of trade and shifting profits towards the domestic market at the expense of foreign trade partners. Countries endogenously form into regional trade agreements or global free trade in a framework where any agreement must be sustained by repeated interaction. A crucial parameter determining the degree of regionalism is product variety. I demonstrate that for a given trade cost and discount factor, increases in product variety leads to greater scope for global free trade relative to regional trade agreements.