I haven't read them, but I was curious if it was an academic vs casual deal as that's fairly common and you can usually tell with the publishers.

However, just looking them up quickly to check that I see one is subtitled "1776-1787" and the other "1789-1815" so while close in area, one seems to be a continuation of the other chronologically.

An American Historian might have to fact check me here, but 1776 to 87 would cover the American Revolution and the Articles of Confederation (the first US Constitution) up until around the Constitutional Convention in 1787 which set to revise the Articles (but in reality started writing the new Constitution) while the second book would begin in 1789 when the US Constitution (the one presently used) was put in effect up until the end of the war of 1812, a period which saw a lot of early ideas of US Government get tested and altered with experience -- such as the creation of a standing military. So both, in my mind, would show the reasons for how both constitutions were created, and how they evolved and discussions around them continued in each one's early years.

So unless those subtitles are very misleading, I imagine that's what Wood is doing there.