The expansion of international trade has been a powerful engine driving economic growth in Western nations over the last two centuries. At the same time, it has provoked an enormous amount of internal political conflict, since trade has disparate effects on different sets of individuals within an economy. Although conflict between "winners" and "losers" has been a constant in trade politics, the character of the political coalitions that have fought these battles--the nature of the societal cleavages that the trade issue creates--appears to have differed significantly across time and place.
Consequently, the literature on the political economy of trade has developed something of a split personality. Many scholars, following in the grand tradition of E. E. Schattschneider, have focused on the political role of narrow industry groups or "special interests" in the policymaking process.  This approach has been prominently adopted by Peter Gourevitch and is common to quantitative studies of trade barriers inspired by the "endogenous policy" literature in economics.  In contrast, Ronald Rogowski has famously examined broad factoral or class coalitions in a range of historical contexts, highlighting political conflicts among owners of land, labor, and capital over the direction of trade policy.  Other analysts, drawing distinctions between owners of multinational and other types of capital, or between skilled and unskilled labor, have made similar assumptions about the centrality of class cleavages in trade politics. 
Empirical evidence suggests support for both approaches. The lobbying free-for-all among industry groups that led to the U.S. Smoot-Hawley Tariff Act in 1930 lives in infamy, and most accounts of contemporary U.S. trade politics indicate that such groups have played a prominent role in recent battles over the North American Free Trade Agreement and the General Agreement on Tariffs and Trade (GATT). Historical accounts of trade politics in a variety of nations--in particular, France during the nineteenth century--reveal that these kinds of industry-based cleavages have a long and robust ancestry.  But examples of class-based cleavages are also familiar to most readers. Perhaps most famously, workers in nineteenth-century Britain, taking on the ruling Tories and the landed elite, aligned with capitalists to provide mass support for freer trade and the Anti-Corn Law League. A similar kind of contest developed in the United States after the Civil War--this time between pro-trade farmers and protectionist urban classes--and led to a Republican tariff in 1890 that was denounced by Democrats as the "culminating atrocity of class legislation."
That both class and group approaches have found empirical support in a variety of contexts suggests the need for a way to bridge the gulf between them that would specify the conditions under which one is more appropriate than the other. To this end I apply the standard economic theory of trade to highlight the importance of inter-industry factor mobility--that is, the ease with which owners of factors of production (land, labor, and capital) can move between industries in the domestic economy. If factors are mobile between industries, the income effects of trade divide individuals...