That ye may eat the flesh of kings, and the flesh of captains, and the flesh of mighty men, and the flesh of horses, and of them that sit on them, and the flesh of all men, both free and bond, both small and great.
Verses 17 and 18 are announcing that a major slaughter, the battle of Armageddon, is about to take place. This is how the seven year period ends and the millennium begins.