Mark Tushnet has an interesting post on how constitutional law changes, focusing especially on the 1930s and the "switch in time." But there is a body of work on the Court that tends not to fit within the framework of the internalist/externalist debate, taking up the question of the impact of war on American legal history.
Another approach to the question of how constitutional law changes is reflected in works like Geoffrey Stone, Perilous Times: Free Speech in Wartime. Stone essentially argues that constitutional law changes to be more restrictive of rights during wartimes, and then basically changes back after wartimes are over (the idea of the swinging pendulum). His thesis is contingent upon the assumption that there are different kinds of time in American history (wartime and peacetime), and he argues that peacetime makes up 80% of the history of the nation.
But Mark Brandon sees American history in a different way, with military conflict, not peacetime, making up 80% of the nation’s history. From Brandon’s perspective, this doesn’t mean that war doesn’t change constitutional law. Instead, he argues that it changes it in a different way. The impact is not cyclical, but instead the impact of war on the state (and therefore on constitutional law) increases over time. This is consistent with a body of work on war and statebuilding, e.g. Katznelson and Shefter, Shaped by War and Trade.
Bringing in Mark Tushnet’s framework, these might both be viewed as “externalist” accounts, although I think most good legal history pays attention both to developments external to the caselaw, and developments within legal thought and caselaw. But the scholarship on war helps us to see that many "externalist" accounts are not externalist enough -- or perhaps there are two versions of externalism: domestic accounts, and accounts that address the U.S. role in global affairs. (For a broader view on debates about the Court and the constitution during the late 1930s, bringing in the wartime context, see David Bixby, “The Roosevelt Court, Democratic Ideology, and Minority Rights: Another Look at United States v. Classic,” 90 Yale Law Journal 741 (1981).)
I wonder whether Mark’s own work intersects both approaches to the impact of war. Overall, his collection The Constitution in Wartime seems to work within the assumptions of the cyclical model of war's impact, though one of Mark’s contributions to that volume suggests that perhaps cycles no longer work after 9/11, since the post-9/11 environment seems more like an ongoing condition than a temporally confined “wartime.” But Mark’s article Defending Korematsu resonates with the literature on war’s ongoing, cumulative impact, since he argues that a “process of social learning” happens in the context of war-related cases like Korematsu, impacting the Court in the future, perhaps through less excessive judicial over-reaching.
For my initial take on this, focusing especially on a critique of ideas about war in works like Stone’s, and largely agreeing with Brandon, see Law, War, and the History of Time (forthcoming California Law Review, Oct. 2010).