AMHERST, Mass. — Evangelical churches today can be found in almost every neighborhood in Latin America — and they are transforming politics like no other force. They are giving conservative causes, and especially political parties, new strength and new constituencies.

In Latin America, Christianity used to be associated with Roman Catholicism. The church held a near monopoly on religion until the 1980s. The only challenge to Catholicism was anticlericalism and atheism. There has never been another religion. Until now.

Evangelicals today account for almost 20 percent of the population in Latin America, up from 3 percent three decades ago. In a few Central American countries, evangelicals are near majorities.

Evangelical pastors embrace varied ideologies, but when it comes to gender and sexuality, their values are typically conservative, patriarchal and homophobic. They expect women to be completely submissive to their evangelical husbands. And in every country in the region, they have taken the strongest stands against gay rights.