Becker-Becker-Schwarz say in the discussion of references to their chapter on flux compactifications:
Flux compactifications were introduced in Strominger (1986) and De Wit,
Smith and Hari Dass (1987) as a generalization of conventional Calabi–Yau
compactifications. Such compactifications include a warp factor, so that the
ten-dimensional metric is no longer a direct product of the external and in-
ternal space-time. No-go theorems implied that in most cases such theories
reduce to ordinary Calabi–Yau compactifications. However, with the devel-
opment of nonperturbative string theory and M-theory, it became evident
that the no-go theorems could be circumvented. Flux compactifications were
first studied in the context of M-theory in Becker and Becker (1996) and in
the context of F-theory in Dasgupta, Rajesh and Sethi (1999). Giddings,
Kachru and Polchinski (2002) explained how flux compactifications can give
a large hierarchy of scales. Grana ̃ (2006) reviews flux compactifications.
I have said a few words about Strominger (1986) earlier. Next I intend to take up De Wit, Smith and Hari Dass (1987).