Conscription is the mandatory enlistment in a country’s armed forces, and is sometimes referred to as “the draft.” The origins of military conscription date back thousands of years to ancient Mesopotamia, but the first modern draft occurred during the French Revolution in the 1790s. The United States instituted conscription during the Civil War, which led to a series of bloody draft riots. Resistance to the draft, as managed by the Selective Service in the United States, reached a historic peak during the Vietnam War.Before the existence of a warrior class or military elite, Babylonian kingdoms employed a system of conscription called ilkum, in which laborers owed military service to royal officials for the right to own land. Provisions for ilkum were created under the ancient Code of Hammurabi, one of the earliest and most complete legal codes, instituted under Babylonian King Hammurabi.
Similar systems of military conscription were popular in feudal Europe throughout the Middle Ages. Land-owning peasants often were required to provide one man per family for military duty.
I'm going out on a limb here and figuring that you're talking about a specific poster that rings a bell. Basically, it portrays the Germans as evil people, and inspires young British men to enlist in the army to fight them.