World War I left a long and painful legacy. (Germany only just finally paying off its reparations payments in... 2010!) The vindictive terms of the Versailles Treaty led to the rise of Hitler and World II. And hasty decisions made over the disposition of territories that made up the former Ottoman Empire left the Middle East unsettled and resentful of western interference. Sound familiar? One of the opportunities in teaching World War I, therefore, is to explore the significance of a good peace. Winning a war is only half the battle. When the war-ending treaty is not well constructed, generations down the line pay the price.
You might also want to explore with your students the many ways in which nineteenth-century ideas about war confronted the twentieth-century realities of warfare during World War I. Older, perhaps obsolete ideas about civilian casualties and the rights of neutrals ran into the harsh, indiscriminate dangers of modern weaponry.