WWI involved many European powers led by czars, kings, and kaisers. Major battles occurred on the western and eastern fronts, including the battles of Verdun, Somme, Ypres, and Marne. Trench warfare led to millions of soldiers living in networks of trenches. Russia eventually left the war due to heavy losses and unrest. The war ended with an armistice in 1918. The resulting Treaty of Versailles placed heavy blame and reparations on Germany and adjusted European borders.