Complex sentence: The Confederates of Schwyz, supported by the Confederates of Uri, feared for their autonomy, but were not supported by the Confederates of Unterwalden, who expected the army to approach from the west near the village of Arth, where they had erected fortifications.
Split into simpler sentences: The Confederates of Schwyz were supported by the Confederates of Uri, who feared for their autonomy. They were not supported by the Confederates of Unterwalden, who expected the army to approach from the west near the village of Arth, where they had erected fortifications.