Colonial documents indicate that at the time of Spanish conquest in 1524 the Izalcos polity of Nahua-speaking Pipil, whose heartland lies in the Rio Ceniza Valley of western El Salvador, was a thriving economic and political power. This region became a jewel in the Spanish Crown due in part to prodigious cacao production. This dissertation presents the results of an intensive regional survey, test excavations, lithic and local and imported ceramic analysis, and transcription of a local archive in order to assess key elements of the Izalcos political economy before and after conquest. Data show that the Pipil were central actors in Late Postclassic regional integration, which pre-positioned the Izalcos within the world genesis of capitalism and structured Spanish colonialism Each documentary, settlement, and artifactual dataset was evaluated separately for its unique insights. Thus, the archaeological data were not 'handmaidens' to historic data, or vice versa, but instead provide different perspectives on the same processes of Izalcos political economy. Sixteenth- to nineteenth-century documents from the Caluco archive and other historic data present strong evidence that the Izalcos Pipil had typically Nahua social and political institutions. These Nahua principles are demonstrated in inter- and intrasite organization and provide part of the logic for the distribution of Pipil settlement in Mesoamerica. The other essential component for understanding Pipil settlement structure is their engagement in the expansive trade network that reached into central Mexico The Izalcos region's importance in long-distance trade was not diminished after Spanish conquest. Pipil concepts, institutions, and boundaries structured Spanish political and economic organization, nevertheless the Spanish rationalized the landscape so that wage labor emerged. This new local market of production, consumption, and speculation, however, was not easily molded by the preferences of a colonial state or even the world-system. The Manila galleon trade was a prime catalyst for Mexico to consolidate power by moving the route of New World trade across the isthmus, but the dispersal of porcelain and majolica in the project area suggests that contraband trade thwarted the Crown's efforts. In each phase, Izalco-centered interests had a gravity the world-system could not escape