By the time the '90s dawned, the X-Men were the biggest comics in the world. The '70s had brought them back to prominence, the '80s had seen them rise to top, and the '90s were basically the victory lap. The X-Men had slowly but surely climbed the ladder and got to a point where the old mainstays of Marvel - Spider-Man, the Avengers, and the Fantastic Four - were appearing in X-Men crossovers. The X-Men were the main draw for the comic industry and Marvel put the best talent possible on the books. Uncanny X-Men became the flagship of not just Marvel comics, but the entire comic industry.
Source：https://www.cbr.com/xmen-1990s-age-apocalypse-history-explained/
