An overflowing population and warlike arms for all--here we have the conditions for migratory conquest. On these conditions the Celtic migrations were based. The spread of these conditions to the Germans led to the later Germanic expansion, and their further spread brought about the Slavonic and Turanian migrations which drove the Germans down upon the subject peoples of Rome, peoples whose power of resistance and will to defend themselves had been already broken by that Roman policy so frankly described by Tacitus. Just as the universal subjection of science and invention to the purposes of warfare has reduced Europe to its present condition, so the universal possession of iron made Europe in the third and fourth centuries a scene of universal war. Though Ireland was fortunately untouched by the great migratory movements of the Continent in that age, these movements reacted on Ireland by weakening the neighbouring provinces of the Empire. The raids on Britain and Gaul for booty and captives--raids from which, as I have argued, the Irish got their new name of Scots--were followed by Irish settlements on various points of the British coast. The conquest of eastern Meath or Bregia by the kings of Connacht and Uisneach forced a part of the population to migrate, and one body of the migrants settled in Demetia, in the south of Wales. We can safely place the conquest of Bregia in the second half of the third century, but it does not follow that the settlement in Wales was made at the same time, for the story of the Déisi migration makes it appear that the expelled population remained for many years in Leinster before the settlement in Munster. There may have been a similar delay before their kindred crossed over to Wales. In south-western Britain, there was also an Irish colony, apparently from Munster and headed by princes of the Eoghanacht dynasty which displaced the earlier line of the Iverni. Cormac's Glossary mentions in the Cornish region a stronghold named Dinn Map Lethan. This name, a mixture of Cymric and Gaelic, means the fortress of the Sons of Lethan. The Ui Liatháin, or descendants of Liathán, were one of the principal septs of the Eoghanachta, and their territory adjoined the Munster coast in the district immediately to the west of the Déisi.