Vassals and serfs worked the manor year in and year out, bound by law to a lifetime of labor. But when war broke out between England and France in 1337, both nations undertook an unprecedented military buildup. This marked the start of the Hundred Years' War, a series of intermittent conflicts that lasted until 1543. In both countries, the army swelled its ranks with feudal laborers, undermining the manorial system while increasing the value of commoners by teaching them much-needed military skills.