Complex sentence: For two days he waited in the valley for the Munros and Rosses, but waiting for them was his biggest mistake as the clans had sided with the Scottish Covenanter Government, and Argyll had already set his counter plans in operation.
Split into simpler sentences: For two days he waited in the valley for the Munros and Rosses. Waiting for them was his biggest mistake as the clans had sided with the Scottish government, and Argyll had already set his counter plans in operation.