For more than 3,000 years, a warrior on horseback or horse-drawn chariot was the ultimate weapon. Time after time, from Asia to Europe to the Americas, the use of horses in war has changed the balance of power between civilizations. When people with horses clashed with those without, horses provided a huge advantage. When both sides had horses, battles turned on the strength and strategy of their mounted horsemen, or cavalry. Horses continued to define military tactics well into the 1900s, until they finally became outmoded by machine guns, tanks, airplanes, and other modern weapons.