By 1916, the First World War has become a stalemate. The battlefields of Europe have been dug into 800 kilometres of trenches. Men are dying, but no ground is being won or lost. On July 1, 1916, 150,000 Allied troops - including thousands of Canadians and Newfoundlanders - go over the top in an attempt to open up the western front. The result is a bloodbath. In this clip from the 90th anniversary of the Battle of the Somme, historian Martin Gilbert describes the futility of "The Big Push."