Problems of unity can affect an armed opposition group at many stages of its existence—during the war, in peace negotiations, and in its transition to political party. This article assesses how internal divisions affected the performance of the Farabundo Martí National Liberation Front (FMLN) in El Salvador. It finds that while the FMLN suffered significant internal divisions in the early years of the war, it remained remarkably unified from 1983 on. Significant divisions began to appear during the later war years but were not exacerbated until after the war's conclusion, when repeated fracturing occurred. The FMLN began to present itself as a programmatically coherent party only in 2005, and this ideological homogeneity allowed it to establish a series of partnerships with moderate, non-revolutionary sectors of Salvadoran society and to achieve victory in the 2009 presidential elections.