She is professor of history at the University of Toronto and the author of the new book, Paris 1919: Six Months That Changed the World, about the Peace Conference after World War I in which delegations from around the world convened to find an alternative to war. During the six months of the conference, new boundaries were drawn up in the Middle East. Out of that conference Iraq was born, and was for a time under British control. MacMillan's book, published under the title Peacemakers in England, was the winner of the Samuel Johnson Prize.