The Frankfurt School was a group of philosophers and social critics in Germany that rose to prominance after the War. They worked on Marxist and Hegelian thought, and along with Derrida and the "postmodernists" have been subject to various conspiracies that they were "destroying western civilization", often even being lumped together, even though they had little in common.

One thing Derrida in particular is accused of is making everything "subjective", the Frankfurt School might even get accused of this themselves, even though a lot of their work is directly opposed to this. They, in fact, pointed out the under modern capialism "reason" had taken on a meaning of technical reason, or subjective reason. "Rationality" was using your intellence to achieve your aims, rather than participating in a sort of broad Hegelian rationality, where we advance human thought in general. So a game theorist, for example, might point out that there are instances where everyone is behaving "rationally", but it culminates in an irrational result. For people like Marcuse, this kind of thing has lost the grander meaning of the term "rationality". Under Capitialism in America, everyone became isolated and encouraged to be "rational" by using their intelligence to succeed by making as much money as possible. People will even say stuff like that the Media is only behaving rationally by maximizing their profits by running clickbait articles to get the most traffic, rather than actually reporting serious news and informing the population. Well, this is a very odd sense of what rationality is, and would have been very foreign to how people like Kant and Hegel used the term. Reducing rationality to an instrumental and subject force creates a society where random, chaotic market forces of "rational" consumers drives the entire society, with no human rationality being applied to what we should be doing in the larger sense. So you have rationality itself responsible for the quite irrational actions of our society, such as consuming so much that we destroy the planet.

Rick Roderick has a good lecture series that is accessible on some of these thinkers, on YouTube.