The Sentinels assumed dictatorial powers over all beings, in the late 21st Century. This continued until Summers came and forged an alliance between humans and mutants to bring the Sentinels down. Almost as soon as the rebellion succeeded, that alliance started to break apart, especially since Summer was no longer there to keep it going. Mutants wanted to move out of the camps and make better lives, but over and over they were met with hostility and driven away.
Some more radical mutant groups, such as the Exhumes, led by a literal fireband named Daemon, met hate with hate. With Summers gone, Daemon listened to no one except his own dark soul. Even during the rebellion, Summers found it difficult to keep him and the Exhumes in line. At first, it was mere raids, but then he and his Exhumes destroyed the human settlement near Del Ray. That brought the Council back into session, and nearly at war with one another.
The X.S.E was formed; their mission was to keep alive the fragile dream born so many years ago by one man, Professor Charles Xavier. The dream was of a world where humans and mutants could live in harmony. The tattoo of the "M" over the right eye that once marked all mutants as outcasts was turned into a badge of honor. When the cadets graduate they would earn their "M" that would indicate that they were members of the X.S.E.
The time traveling X-Men, Bishop, was the youngest cadet to graduate the X.S.E Academy and become an officer. A year later Bishop's sister, Shard, to that honor away when she graduated..