BRUSSELS (AP) — At a site where their countrymen once slaughtered each other with machine guns, artillery and poison gas, the leaders of Britain, France, Germany and other European nations commemorated the 100th anniversary of World War I and vowed Thursday to preserve peace on the continent.

About half a million people died in the arduous battles in the flat, often muddy killing grounds in and around the small Belgian city of Ypres in western Flanders between 1914-18, one of the sites that reflected the savagery of what became known as “The Great War.”