He criticized then-current approaches to history which viewed medieval institutions and legal practices as primitive antecedents of a supposedly more advanced form of political community, namely the constitutional nation-state.
(The radical devaluation of the idea of political liberalism and the centrality of the democratic nation-state could also be found in the writings of the fascist legal theorist Carl Schmitt, whose work Brunner followed closely and cited in his books.)
Although his intellectual efforts were clearly aligned with the Nazis, Brunner was apparently not personally antisemitic and even used his own resources and political connections during World War II to protect the mother of a colleague, Erich Zöllner [de], who was part-Jewish and would have been subject to deportation.
Brunner, along with historians like Karl Bosl, Walter Schlesinger, Theodor Schieder and Werner Conze—all of whom supported, or were openly sympathetic to, Nazism in one way or another before and during the war—dominated the theory and teaching of medieval social history in post-war Germany and Austria.
[9] A few scholars, like the Czech medievalist František Graus, attempted to raise questions about the ideological implications of their methods and theories, as well as the tenability of some of their historical interpretations, but failed to effectively displace them from their position in the academy.
Others, like the Göttingen historian Otto Gerhard Oexle, have argued that Brunner's work should be understood in the broader context of historical attitudes in the 1920s and 30's and not simply dismissed as Nazi propaganda.
This applies to the notion of the whole house, in which Brunner saw the key term to describe the basic units of premodern societies, or to his definition of the feud, which he understood as a central form of medieval politics.
From today's perspective, it is emphasized in this context that Brunner set an “ideal of integration” with his concept of the whole house and thus largely excluded conflicts from the consideration of medieval history.