The main factor that led to the Second Great Awakening was the Enlightenment and the decrease in religious fervor that went along with it. The Second Great Awakening is seen as a response to or a backlash against those developments.
During the time before the Second Great Awakening, Enlightenment ideas such as Deism and Unitarianism had been gaining popularity in the US. These were ideas that generally had less emotion to them. They saw God as disinterested (Deism) or simply a kind and loving father (Unitarianism). Neither had an "old-time religion" feel to them that emphasized an emotional connection to God or a deep fear/awe of him.
Historians argue that this swing of the pendulum towards liberalism in religion led to a reversal. The pendulum swung back towards more traditional views of religion. This reversal was the Second Great Awakening.
In this way, the Enlightenment move towards liberal, modern ideas is what sparked the Second Great Awakening.