As the world marks Victory Day, when decades ago the threat of Nazi Germany – the threat to the progress of all mankind – was defeated by the allied forces of the West and the Soviet Union, the question of how the three leaders, Stalin, Roosevelt and Churchill, so different in their views and agendas, were able to overcome their differences and unite together to crush the great enemy, still stands. Today, when the world again needs nations to put aside their squabbles and fight against global terror, one should wonder how the great alliance against Nazism was forged – and what role the personalities of the three leaders played in that cooperation. Was it just necessity that drove the Soviet Union, the US and Britain together, or would the united front against Hitler have been impossible if not for the three men who found common ground between each other – and steered the world toward peace and the end of war? We ask a professor of modern history at University College Cork, in Ireland, a renowned World War II historian, and author of numerous books on the Soviet role in the war. Geoffrey Roberts is on Sophie&Co today.