He led a crusade against Finns in 1202 with his brother[3] and lobbied the Pope for a crusade against the Baltic nations. He eventually received permission to install a bishop in Reval (modern day Tallinn), and in 1219, he accompanied Valdemar II in his war against Estonia. According to an old Danish myth supportive of the Danish imperial expansion, the Danish flag Dannebrog appeared in the sky and fell into the hands of Valdemar II as Sunesen raised his arms and prayed for a Danish victory during the decisive battle.