US History: Chapter 5, Exercise 2 — Possible Solution
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CORRECTION
The chapter's source reports that most modern historians treat slavery as the
central cause, citing the states' own secession documents. It says the
"Progressive school" once argued for economic causes but modern historians
reject that, and that "states' rights" was itself "an ideology formulated and
applied as a means of advancing slave state interests," not an independent
cause.

REWRITE
"Most historians identify slavery as the central cause of secession; the idea
that states' rights was a separate cause is treated by modern scholars as
part of the pro-slavery argument itself."