At the heart of feudalism was * a. the knight, who was the enforcer of the lord and a protector of the lord’s lands.
B. serfdom, which meant that all non-vassals labored to support the serfs.
C. the grant of serfs made to loyal vassals, which was known as a fief.
D. vassalage, which meant warriors swore loyalty to a lord, who in turn took care of their needs.

world war i began in 1914, after the assassination of archduke franz ferdinand, and lasted until 1918. during the conflict, germany, austria-hungary, bulgaria and the ottoman empire (the central powers) fought against great britain, france, russia, italy, romania, japan and the united states (the allied powers). to new military technologies and the horrors of trench warfare, world war i saw unprecedented levels of carnage and destruction. by the time the war was over and the allied powers claimed victory, more than 16 million people—soldiers and civilians alike—were dead.

explanation:

c. the passage of the fifteenth amendment