Cosmic acceleration in Kaluza-Klein supergravity

String theory is one of the most promising attempts in constructing a consistent quantum theory of gravity and other forces in Nature. The rough idea behind string theory is fairly simple, there are vibrating strings and the different vibrational modes give rise to many particles and forces. The mathematical construction of the theory is complicated and unfinished, but perturbatively we have a good description of string theory. The full non-pertubative description is still to be formulated. In the second half of the nineties new insights have seen the daylight in the understanding of the non-pertubative formulation of string theory that was dubbed M-theory. For instance, it became clear that there must not only be strings but also membranes and even higher dimensional objects, called branes in short. Since the last ten years of string theory (or M-theory)-research is a growing interest that lies outside of the mathematical formulation of the theory but more in the phenomenological aspects of string theory. This comes from the realization that if string theory describes our world it should account for the low-energy phenomena today, which include particle physics on a small scale and cosmology on a large scale. This thesis concerns the second part, the relation between string theory and cosmology.