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Viking period
From the 9th to the 12th century Viking/Norse-Gael Dublin in particular was a major slave trading center which led to an increase in slavery.[4] In 870, Vikings, most likely led by Olaf the White and Ivar the Boneless, besieged and captured the stronghold of Dumbarton Castle (Alt Clut), the capital of the Kingdom of Strathclyde in Scotland, and the next year took most of the site's inhabitants to the Dublin slave markets.[4]
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Slavery became more prevalent throughout Ireland the 11th century as port cities built up by Vikings flourished, with Dublin becoming the biggest slave market in Western Europe.[9][5] Its main sources of supply were the Irish hinterland, Wales and Scotland.[9] The Irish slave trade began to decline after William the Conqueror consolidated control of the English and Welsh coasts around 1080, and was dealt a severe blow when the Normans abolished slavery in 1102.[10][6][9][11] The 1171 Council of Armagh freed all Englishmen and women who were enslaved in Ireland.[12] It was clear from the Decree of the Council of Armagh that English were selling their children as slaves. "For the English people hitherto throughout the whole of their kingdom to the common injury of their people, had become accustomed to selling their sons and relatives in Ireland, to expose their children for sale as slaves, rather than suffer any need or want."[13]