Complex sentence: While Novgorod was unsuccessfully trying to subdue Karelians, Sweden was successfully doing the same with the neighbouring Finnish tribes and in 1293 AD Swedes raided Karelian lands and successfully founded a castle of Vyborg on the site of an ancient Karelian settlement.
Split into simpler sentences: While Novgorod was unsuccessfully trying to subdue Karelians, Sweden was successfully doing the same with the neighbouring Finnish tribes. In 1293 Swedes raided Karelian lands and successfully founded a castle of Vyborg on the site of an ancient Karelian settlement.