The formula for gunpowder was discovered in China in 800 AD. Known as 'fire-drug', its origin was the alchemists' search for an immortality elixir, and it was initially a medicine not an explosive; but the Chinese went on to develop every type of weapon that ever used gunpowder - incendiaries, bombs, rockets, cannon and hand-held guns - as well as fireworks. For 400 years, the Chinese kept gunpowder to themselves, until a Mongol soldier leaked the secret to the Islamic world. The Ottoman empire was built on gunpowder, after the spectacular capture of Constantinople using new siege tactics, while the Moghuls conquered India with muskets and artillery mounted on 700 carts held together with ox-harnesses. The use of gunpowder in Europe was inhibited by a shortage of saltpetre, but archers soon gave way to gunners, while gunpowder destroyed the last vestiges of feudalism and changed the balance of power in the medieval world. Small groups of Europeans with guns, rapidly subdued vast numbers of first native defenders in the New World, while in the Far East Japanese, muskets and cannons defeated the Koreans on land, but the Korean armoured ships were triumphant at sea.