Up until the late 70's of the twentieth century it was widely held, in science in general and the humanities in particular, that there is a clear distinction between different disciplines and fields of knowledge. This means the historians ought to deal and are dealing strictly with history while psychologists deal with psychology and literature people restrict themselves to what is conceived as literature. This taxonomic division was manifested and reflected in the structures of universities as we know the, i.e. faculties, departments etc. which trained professionals and researchers in distinct domains in accordance with the accepted categorization.
All this changed when more and more universities began to open departments of interdisciplinary studies, with "cultural studies" bearing the lead. These departments merge different disciplines and have led to the "migration" of tools and theories from one domain to another.
A number of factors stand to account for the interdisciplinary turn:
One of the foremost causes of the interdisciplinary turn is without a doubt what was dubbed as "the linguistic turn" in humanities. This turn originated in European thought that travelled to the Anglo-Saxon world and gained hold in universities across America. The linguistic turn is associated with thinkers such as Ferdinand de Saussure, Jacques Derrida, Michel Foucault and Roland Barthes which have eventually led to the understanding of culture as a system of lingual construction and the famous Derrida quote of "there is nothing outside the text". In the post-structuralism era language was perceived as constitutive rather than reflective and was therefore studies and questioned as an object in itself, granting the literature researcher the freedom to legitimately deal with a legal text and even exact sciences.
These developments have led to the rise of constructivist approaches in the humanities and discussions regarding the role of ideology and power structures and apparatuses in the scientific field and methods that originated from literature studies have now been put to use in order to reveal and expose these mechanism. Objectivity was dismissed and war was declared on anyone pertaining to be objective. This also led to the perception of the academic field as a political arena with the rise of "posts" of sorts such as post-feminism and post-colonialism. The question of which texts are presented in the foreground and which are silenced became critical, in all senses.
The interdisciplinary turn raises a few interesting questions regarding the academic world. One may be inclined to wonder what happens when a researcher from on domain starts developing an interest in a field he is relatively unacquainted and unfamiliar with? Can a literature researcher really have something to offer for the historian? Another question is what happens when concepts, tools and theories from one discipline "migrate" to a different field, do they stay valid or do they coerce reality? Another important question regarding the interdisciplinary turn in the relation between disciplines: do they stay as whole and independent of each other or are they merged into new disciplines? Should the academic world address this trend by engaging in what might be called "meta-disciplinary"?