Complex sentence: They collected Everard Digby and his men at Dunchurch, and the next day raided Warwick Castle for supplies--something that Robert strongly objected to, as it would create "a great uproar" in the country.
Split into simpler sentences: They collected Everard Digby and his men at Dunchurch, and the next day raided Warwick Castle for supplies. This was something that Robert strongly objected to, as it would create "a great uproar" in the country.