A disruption of the Federal Union, heretofore only menaced, is now formidably attempted.

What is meant by "a disruption of the Federal Union" in this sentence?

A. a joining of the northern states with the states that had seceded
B. an attempt by the southern states to form their own government
C. secession, or the breaking away of southern states from the Union
D. an interruption in the arguments between the North and the South