Peterson adapted his dissertation as his first book, The Jefferson Image in the American Mind (Oxford University Press, 1960), which won the 1961 Bancroft Prize for History.
At the end of a decade, he published a lengthy one-volume biography, Thomas Jefferson and the New Nation (Oxford University Press, 1970), which he considered his most important book.
Part of a generation that was admonished in its youth to "remember the starving Armenians," Peterson traveled to Armenia in 1997 as a Peace Corps volunteer and was moved by the country's troubled history.
He begins with the initial reports to President Woodrow Wilson from Henry Morgenthau, Sr., his ambassador to the Ottoman Empire.
Peterson also covers the contemporary period and the continuing campaign by ethnic Armenians and others to convince the U.S. government to officially recognize the actions as genocide, which Turkey has denied.