Star Wars: The Last Jedi. The sequel trilogy has brought the Resistance to its knees, and in Star Wars: The Last Jedi that the Resistance leadership was reduced to so few people that they could all fit aboard the Millennium Falcon.
Making matters worse, The Last Jedi saw Leia desperately reach out to her allies across the galaxy, particularly those scattered across the galactic rim. Poe Dameron insisted that the Resistance's allies would eventually come, but they didn't, and as a result only the intervention of Luke Skywalker allowed the Resistance leaders to escape the First Order at all. Ever since, viewers have wondered; just what happened to all those mysterious Resistance sympathizers?
Star Wars has attempted to explain this away in Maz Kanata's spy network figures out what's going on, and Maz gives the information to Poe Dameron personally.
"We've long suspected that the First Order has been taking children and disappearing people on the margins of the galaxy. But things are escalating now: arresting people on phony trumped-up charges. Small crimes that they've blown up into capital offenses, or charges simply fabricated out of nothing. People going missing in the dead of night, their families having no idea what happened to them. Nighttime raids or picked up off the streets and vanished. And the people most likely to disappear? People with ties to the old rebellion."
Resistance Reborn shines a new light upon the First Order's strategy to take the galaxy. It had always seemed strange that they waited so long to strike, given Star Wars: The Force Awakens marked the moment when they began to act on that information, and even as First Order ships spread across the Republic conquering it, their agents neutralized Resistance allies with lethal efficiency.
Ironically, this plan backfired in the end, because Maz Kanata's network managed to locate the list on Corellia - the same world many of the Resistance allies had been taken to for imprisonment. The Resistance successfully stole the list, and rescued many of them. As a result, their numbers were swiftly replenished. Worse still for the First Order, the list included names to monitor just in case, and the Resistance immediately knew who would be sympathetic to their cause. As a result, over the year, Leia was able to rebuild the Resistance at speed, just in time for the events of Star Wars: The Rise of Skywalker.