Despite “his own visceral contempt for their adherents,” the future supreme leader of the Islamic Republic of Iran, Ayatollah Ruhollah Khomeini, found utility in integrating “the influence of the leftist ideologies that had made such a mark on the Middle East over previous decades” into his revolutionary pitch. That is how Jason Burke, author of the new book The Revolutionists, describes the genesis of what would become the Iranian “red-green alliance” in his epic retelling of how the Marxist militants of the 1970s evolved from Cuban-style communists into socialist pan-Arabists and, eventually, Islamists. Subtly, Khomeini and his deputies integrated the...