The kings appointed their officials from among the members of about 110 aristocratic kindreds. These aristocrats were descended either from native (that is, Magyar, Kabar, Pecheneg or Slavic) chiefs, or from foreign knights who had migrated to the country in the 11th and 12th centuries. The foreign knights had been trained in the Western European art of war, which contributed to the development of heavy cavalry. Their descendants were labelled as newcomers for centuries, but intermarriages between natives and newcomers were not rare, which enabled their integration. The monarchs pursued an expansionist policy from the late 11th century. Ladislaus I seized Slavonia - the plains between the river Drava and the Dinaric Alps - in the 1090s. His successor, Coloman, was crowned king of Croatia in 1102. Both realms retained their own customs and Hungarians rarely received land grants in Croatia. According to customary law, Croatians could not be obliged to cross the river Drava to fight in the royal army at their own expenses.