Complex sentence: Another regiment, the Whatcom Company, was formed of mostly southerners under the command of Captain Graham, and were of the "a good Indian is a dead Indian" persuasion and were bent on a war of extermination.
Split into simpler sentences: Another regiment, the Whatcom Company, was formed of mostly southerners under the command of Captain Graham. This regiment was of the "a good Indian is a dead Indian" persuasion and was bent on a war of extermination.