Complex sentence: Finally on the December 27 the Swedes decided to withdraw, although they made several small attempts to take the monastery by surprise in the weeks to come, as the fortress became an increasingly important center for the local anti-Swedish guerillas.
Split into simpler sentences: Finally on the December 27 the Swedes decided to withdraw. They made several small attempts to take the monastery by surprise in the weeks to come, as the fortress became an increasingly important center for the local anti-Swedish guerillas.