12th century BC, between c.1200 and 1150. It was sudden, violent, and culturally disruptive for many Bronze Age civilizations, and it brought a sharp economic decline to regional powers, notably ushering in the Greek Dark Ages. Historian Robert Drews argues for the appearance of massed infantry, using newly developed weapons and armour, such as cast rather than forged spearheads and long swords, a revolutionizing cut-and-thrust weapon, and javelins. Such new weaponry, in the hands of large numbers of "running skirmishers", who could swarm and cut down a chariot army, would destabilize states that were based upon the use of chariots by the ruling class. That would precipitate an abrupt social collapse as raiders began to conquer, loot and burn cities. The Bronze Age in China traverses the protohistoric and historic periods. Battles utilizing foot and chariot infantry took place regularly between powers in the North China Plain. Iron Age Early Iron Age events like the Dorian invasion, Greek colonialism and their interaction with Phoenician and Etruscan forces lie within the prehistoric period. Germanic warrior societies of the Migration period engaged in endemic warfare (see also Thorsberg moor). Anglo-Saxon warfare lies on the edge of historicity, its study relying primarily on archaeology with the help of only fragmentary written accounts. There are around 3,300 structures that can be classed as hillforts or similar "defended enclosures" within Britain. Hillforts in Britain are known from the Bronze Age, but the great period of hillfort construction was during the British Iron Age, between 700 BC and the Roman conquest of Britain in 43 AD. The reason for the emergence of hillforts in Britain, and their purpose, has been a subject of debate. It has been argued that they could have been military sites constructed in response to invasion from continental Europe, sites built by invaders, or a military reaction to social tensions caused by an increasing population and consequent pressure on agriculture. Endemic warfare In warlike cultures, war is often ritualized with a number of taboos and practices that limit the number of casualties and the duration of the conflict. This type of situation is known as endemic warfare. Among tribal societies engaging in endemic warfare, conflict may escalate to actual warfare occasionally for reasons such as conflict over resources or for no readily understandable reason. Warfare is known to every tribal society, but some societies developed a particular emphasis of warrior culture (such