The distinguished historian C. R. Boxer devoted years of research and reflection on European expansion overseas into the Americas and Asia. In The Church Militant and Iberian Expansion, 1440-1770, his analytical survey of the role of the Portuguese and Spanish missionaries of the Roman Catholic Church in the overseas expansion of the Iberian powers, he finds that the lasting results vary enormously. "They range,"he writes, "from enduring mass conversions in some regions, of which sixteenth-century New Spain is the prime example, to the total failure in other countries, such as Cambodia, where the number of indigenous converts could be counted on two hands."

Considering the church as "a human as well as a divine institution,"the author focuses on four types of organizational problems: relations between the regular and the secular clergy; the mission as a frontier institution in many climes and many cultures; the close and inseparable connection between Cross and Crown; and the role of the Inquisition overseas. Boxer finds that "the mere survival of these Christian minorities through the vicissitudes of over three centuries is a tribute to the work of the dedicated missionaries of the Church Militant in times past."