Chapter 9 completes the account of the third constitutional change in the national rule of apportionment. Whereas Chapter 8 described the development of various environmental (or macrolevel) conditions between 1790 and 1860, this chapter analyzes the microlevel (or actorcentered) conditions that effected the abandonment and replacement of the original Constitution's rule of apportionment. This chapter focuses on the sequence of decisions that preceded the wholesale breakdown in the political bonds between the northern and southern states. It also provides a brief account of the formalization of a new national rule of apportionment in the aftermath of the American Civil War.

The structural developments described in Chapter 8 offer no immediately obvious long- or short-term sectional differences that necessitated a constitutional crisis between northern and southern states in 1861. Since 1790, every state had reaped significant benefits under the constitutional Union established in 1787. In addition to sharing generally peaceful domestic and external constitutions, high rates of demographic growth, and sustained (although uneven) economic development, the principal interests within both sections had fashioned similar state governmental institutions and conceptualizations of representation, and they both had success in using the national government to promote or protect their particular interests.

During the first half of the nineteenth century, relative differences among the sections grew more prominent in several areas, although these differences were often mitigated by shared national experiences or by other more deeply embedded political commitments and capacities.