A good starting point may be the roots of knowledge in Europe during the time of Enlightenment (meaning we could now kill our enemy on a larger scale), and how this fed into modernism. These issues are discussed in broad terms in the following article on positivism and post-positivism (other related schools of thought are objectivism, realism, ....)
It gets really hairy from here on down - so I leave you with a few sites where you can lose youself.
A broad overview of Theoretical Paradigms: Cultural Studies, Ethnic Studies, Feminism, Formalism, Marxism, Psychoanalysis, Structuralism, Performativity Theory, and Post-Structuralism http://www.sou.edu/English/IDTC/Paradigm/ovrview.htm
A nice synoptic site covering "Contemporary Philosophy, Critical Theory and Postmodern Thought Resources", a link to "what is post modernism", and reports on the following people (and group): Theodor Adorno, Louis Althusser, Roland Barthes, Michael Bakhtin, Jean Baudrillard, Walter Benjamin, Maurice Blanchot, Kenneth Burke, Jacques Derrida, Gilles Deleuze, Terry Eagleton, Stanley Fish, Michel Foucault, Frankfurt School, Felix Guattari, Jurgen Habermas, Donna Haraway, Martin Heidegger, Max Horkheimer, Edmund Husserl, Fredric Jameson, Jacques Lacan, Jean Francois Lyotard, Georg Lukács, Paul de Man, Herbert Marcuse, Karl Marx, Maurice Merleau-Ponty, Richard Rorty, Edward Said, Charles Taylor, Ludwig Wittgenstein. http://carbon.cudenver.edu/~mryder/itc_data/postmodern.html by Martin Reider at the University of Colorado at Denver, School of Education.
A lot of ideas and links on qualitative research by Martin Reider at the University of Colorado at Denver, School of Education. http://carbon.cudenver.edu/~mryder/itc_data/pract_res.html