However, after the publication of Revelation as History in 1961, the focus of his research and publication changed direction. The work engendered such a fervent discussion that he felt the need to first engage his critics and later expand the insights of this work in a number of areas. Beginning in 1963, he began to receive regular invitations to the United States, where he offered courses at the University of Chicago, Harvard Divinity School, and Claremont School of Theology.
