During the Middle Ages, German political power was imposed on Slavic populations in the east. This process was accompanied by the migration of Germans into conquered territories, in what is known as the Ostsiedlung. Over time, some Slavic populations were assimilated by Germans, resulting in many Germans acquiring substantial Slavic ancestry. From the 11th century, the German lands came under the domination of the Swabian Hohenstaufen family. The German population expanded significantly during this time. Trade increased and there was a specialization of the arts and crafts. From the 12th century, many Germans settled as merchants and craftsmen in the Kingdom of Poland, were they came to constitute a significant proportion of the population in many urban centers such as Gdańsk.