An overriding query shapes this study. The major political parties in the United States, Canada, and Mexico have profoundly altered their historical positions on foreign trade. In fact, they have exchanged positions. Why did each political party change its orienation towards free trade? What were the causes, and what were the consequences, for the choice of regional versus universal trade liberalization? How have political institutions in each country contributed to these political party flip-flops on free trade? What factors or processes explain how a political party adopts a position on trade, and how governments actually take a stand? This chapter draws on the prior chapters to build a theoretical model attempting to explain the long-term relationship in North America between trade and political party.