Throughout history, great and terrible events have often hinged on chance. Here, historian Andrew Roberts has assembled a team of his prominent colleagues, asking them to consider what might have happened if major world events had gone differently. Amanda Foreman, author of Georgiana, Duchess of Devonshire, ponders what might have happened if Lincolns Northern States of America and Queen Victorias Great Britain had gone to war, as they so nearly did in 1861. George W. Bushs former White House adviser, David Frum, considers a President Al Gores response to 9/11, while Conrad Black wonders how the U.S. might have entered World War II if the Japanese had not bombed Pearl Harbor. Whether its Stalin fleeing Moscow in 1941, as envisioned by Simon Sebag Montefiore, or Napoleon not being forced to retreat from it in 1812, as pictured by Adam Zamoyski, these essays posit a fascinating, sometimes horrifying parallel universe.