Complex sentence: Together with Tiveden to its west and Kolmården to its east, it famously constituted the wartorn frontier between the Swedes in Svealand and the Geats in Götaland during the formation of the Swedish nation in the 13th century.
Split into simpler sentences: Together with Tiveden to its west and Kolmården to its east, it constituted the border between the Swedes in Svealand and the Geats in Götaland in older times. Wars were fought here during the formation of the Swedish nation in the 13th century.