The main thing that this book wants to do is upend any straightforwardly linear notions of development (or modernity), and argue for a single world system, one where apparent "backwardness" or "underdevelopment" in one place is often actively produced by "development" in another. The next step is to connect this notion to literature, which they do by arguing that "world literature be conceived precisely through its mediation by and registration of the modern world-system." (9) Along the way, they spend some time distinguishing this position from other approaches to world literature (especially those of David Damrosch, Franco Moretti, Pascale Casanova, and Wai Chee Dimock). They proceed to examining a number of texts, from a variety of places (though generally in translation), focusing very specifically on how they register the existence of, and their position within, the world-system. Although homage is paid to form, and the authors occasionally gesture towards a notion that certain constellations of development (or rather, positions within the world-system) are strongly correlated with specific literary techniques (unreliable narrators, anti-linear plot lines, meta-narratorial devices), they mostly discuss content.
The book is a useful synthesis of many different ways of talking about socio-economic development and world systems in literary studies, if an occasionally strident one. The argument is very clear and quite easy to follow, which makes it very helpful in terms of framing and positioning one's own approach.