Himmler's War, (2011) ISBN 978-1451637618, deals with what might have happened if Hitler had been killed in 1944, and leadership of Nazi Germany had passed to Himmler, who then adopts a considerably different strategy.
North Reich, (2012) ASINB008BVXZXO, considers if Britain had surrendered to Nazi Germany, and had a fascist regime installed across the Commonwealth and Empire, with Canada becoming a base from which Germany prepares to launch a war against the United States
Rising Sun, (2012) ISBN 978-1451638516, is set in the aftermath of a Japanese victory at the Battle of Midway, in which Japan launches an invasion of Alaska and conducts carrier-based airstrikes against the West Coast of the United States.
1920: America's Great War, (2013) ISBN 978-1451639315, in which the United States remained neutral during World War I, resulting in victory that leaves Germany in control of most of Europe. Germany then uses Mexico as a base to launch an invasion of the United States.