Complex sentence: By the 11th century, Scandinavian heros are frequently chronicled as being slain while fighting pirates on the eastern shores of the Baltic Sea in retaliatory raids which eventually lead to German, Danish and Swedish participation in the Northern crusades and the conquest of Estonia.
Split into simpler sentences: By the 11th century, Scandinavian heros are frequently chronicled as being slain while fighting pirates on the eastern shores of the Baltic Sea in retaliatton for pirate raid. This eventually lead to German, Danish and Swedish participation in the Northern crusades and the conquest of Estonia.