The Premise.
It was a new age.
It was an age of peace. Of prosperity. It was an age when mutants and humans would work together.
After the defeat of the Mutant Liberation Front by the X-Men, Charles Xavier sat down with world leaders and helped to negotiate a ground-breaking treaty in Philadelphia, Pennsylvania. The Treaty of the Liberty Bell ensured that Mutants would be given equal rights in human society, with the condition that all militant groups such as the X-Men be permanently disbanded.
In the United States, Xavier's School for Gifted Youngsters, commonly known as the Mutant Institute, remained open as a place for parents to send children who wanted to gain a better understanding of how to control their powers, and many of the former X-Men remained on at the school as teachers and mentors to the young students. Now that the school was well-known to the public, government agents conducted regular check-ups of the grounds, ensuring that no mutant armies were forming and that Xavier was upholding his promise of pacifism and moderation. Pleased with his accomplishments, Xavier himself left the school to pursue further research and allow his school to flourish in its own way, without his constant watch.
Of course, treaties don't solve everything. Old grudges still remain. Some of the former X-Men are growing restless. Rumors of underground resistance are beginning to surface. And despite the official line of civil rights spewed by the governments, things have a long way to go before equality is reached.
Such is the new age of mutants and humans.
Such is life at The Mutant Institute.