Māori warriors were held in high esteem. One group of Polynesians migrated to the Chatham Islands, where they developed the largely pacifist Moriori culture. Their pacifism left the Moriori unable to defend themselves when the islands were invaded by mainland Māori in the 1830s. They proceeded to massacre the Moriori and enslave the survivors. Warrior culture also developed in the isolated Hawaiian Islands. During the 1780s and 1790s the chiefs and alii were constantly fighting for power. After a series of battles the Hawaiian Islands were united for the first time under a single ruler who would become known as Kamehameha I. After gunpowder weapons were first developed in Song dynasty China (see also Technology of Song Dynasty), the technology later spread west to the Ottoman Empire, from where it spread to the Safavid Empire of Persia and the Mughal Empire of India. The arquebus was later adopted by European armies during the Italian Wars of the early 16th century. This all brought an end to the dominance of armored cavalry on the battlefield. The simultaneous decline of the feudal system – and the absorption of the medieval city-states into larger states – allowed the creation of professional standing armies to replace the feudal levies and mercenaries that had been the standard military component of the Middle Ages. In Africa, Ahmad ibn Ibrihim al-Ghazi, was the first African commander to use gunpowder on the continent in the Ethiopian–Adal War, that lasted for fourteen years (1529–1543). The period spanning between the 1648 Peace of Westphalia and the 1789 French Revolution is also known as "Kabinettskriege" (Princes' warfare) as wars were mainly carried out by imperial or monarchics states, decided by cabinets and limited in scope and in their aims. They also involved quickly shifting alliances, and mainly used mercenaries. Over the course of the 18th-19th centuries all military arms and services underwent significant developments that included a more mobile field artillery, the transition from use of battalion infantry drill in close order to open order formations and the transfer of emphasis from the use of bayonets to the rifle that replaced the musket, and virtual replacement of all types of cavalry with the universal dragoons, or mounted infantry. The Military Revolution is a conceptual schema for explaining the transformation of European military strategy, tactics and technology in the early modern period. The argument is the dramatic advances in technology, government finance, and public administration transformed and modernized European armies, tactics, and logistics.