The Breach happened, then. That's important because it was Corypheus who did that. He was attempting to return to the Fade to reclaim the Black City. His plan was to use an ancient elven orb to rip over the Veil and cross over. However, the person who gave him that orb believed the explosion that would result from that ritual would kill him.

Instead, it... Well, you've probably heard? Have you met the Inquisitor yet?