Peter Cooper, from heteconomist, writes about the importance of the State for the operation of Capitalism.
From a methodological perspective, to keep State and Government out of the picture, as a first approximation, is a useful approach to study Capitalism: it simplifies the subject. I would add that during the 19th century such simplification was probably less radical than it may seem to contemporary eyes.
Additionally, Cooper argues that "in debate between the proponents of laissez-faire capitalism and its dissenters, the approach is useful and informative".
However, this approach may have less desirable consequences. Read more at heteconomist