300 years ago, Glint declares the Flameseeker Prophecies, and the Mursaat, frightened of their own destruction foretold in the Prophecies, begin to take steps to ensure that it never happens. They know that it will be a human Chosen who will cause their destruction, but they don't know WHERE the Chosen will come from. Thus, they set into motion the Charr invasion, urging the Charr to destroy the human kingdoms of Ascalon and Orr.
The Charr had initially worshipped the Titans as their ancient gods, but then the Mursaat showed up and insinuated themselves into the Charr religion, resulting in the Mursaat effigies being displayed alongside the Titan ones. The Mursaat give the Charr the magical knowledge necessary to perform the Searing, and at first all seems well.