Where does surplus value come from?

(this was part of a debate on a discussion board against MIM's line. Kasama's series of posts dig into surplus value from various angles and get into the economic behind it all. I actually found these post helpful in understanding surplus value myself)

Kasama's post that deals with: Imperialist export of capital to the third world is crucial to modern capitalism in any ways, but it does not mean that workers WITHIN the u.s. are not exploited or do not produce surplus value.

Kasama's post on : Imperialism, the issue of "the falling rate of profit" and the issue of Finance Capital

Kasama's post on : Contradictions, crisis and the fundamental contradiction

Kasama's post that gets down with the statistics on this issue