Star Trek: Picard jumps ahead in the main timeline of Star Trek to find Captain Jean-Luc Picard years after he's retired from Starfleet. The series also includes a lot of references to Trek history and storylines from different sources, including Star Trek: The Next Generation and Star Trek: Voyager.
But Star Trek: Picard isn't just drawing on the stories told in contemporary series as it expands on the life and career of the legendary captain. It also takes a cue from a somewhat less-likely source: the 2009 Star Trek film directed by J.J. Abrams. Though that movie and its sequels, Star Trek: Into Darkness and Star Trek Beyond, take place in an alternate timeline to tell new stories about the iconic Captain Kirk and the crew of his Enterprise, the story still has some influence on the main Star Trek timeline--and on the events of Star Trek: Picard.
The influence comes from the setup of Star Trek 2009, which established a big change in the Star Trek universe: In the backstory for Abrams' movie, a supernova destroys Romulus, the homeworld of the Romulan Star Empire. Star Trek fans know that the Romulans have been one of the United Federation of Planets' longest enemies. During the events of Star Trek: The Next Generation, which first introduced Picard and his crew, the Federation and the Romulans were in the middle of a tenuous cease-fire, with the territory between them known as the Neutral Zone. Though the Federation and the Romulans sometimes were at odds during the series, for the most part, they left each other alone.
The Romulans were still a threat even well after the end of TNG, however. In Star Trek: Nemesis, the last of the Star Trek movies to feature the TNG crew, some Romulan military leaders planned a massive, devastating attack on the Federation. Picard and the Enterprise crew managed to circumvent that attack and prevent a war, with the help of Romulan commanders who weren't so keen on restarting hostilities.
Cut to Star Trek 2009, which starts its story in the original Star Trek timeline, known as the Prime timeline. In that story, a supernova destroys the Romulan homeworld, and with it, millions (or billions) of Romulan lives. In the movie, Spock (at this point an ambassador) attempts to stop the supernova and save Romulus utilizing a strange substance known as Red Matter, which can be used to create black holes. Spock's plan is to use a black hole to basically suck up the supernova and save the planet--but the star explodes before he can execute his plan, and Romulus is destroyed.
That event leads the commander of a Romulan mining ship, Nero, to chase down and attempt to kill Spock in order to take revenge on him. Instead, however, both Nero and Spock's ships are drawn into the black hole Spock creates, which catapults them back in time. Nero's presence in the past alters some formative events in the life of Captain Kirk, fundamentally altering history--and creating a new alternate timeline for those movies, known as the Kelvin timeline.
But the destruction of Romulus is an event that still occurred back in the Prime timeline, before time travel became a thing (in this context), and Star Trek: Picard picks up after that event. In the premiere episode of the CBS All Access series, we learn that it wasn't just Spock who tried to prevent disaster on Romulus. In response to the planet's impending doom, the Romulans asked the Federation for help in saving its citizens. Some in the Federation were reluctant, but Jean-Luc Picard managed to convince Starfleet to mount a massive rescue effort, and to create an armada of ships to get it done. That was 14 years before the events of the first episode of Picard.
Unfortunately, tragedy struck before the rescue effort got underway. A group of rogue synthetics--essentially, non-sentient androids--attacked Mars and the Federation's Utopia Planitia shipyard, where the rescue armada was utterly destroyed. After that, the Federation refused to help the Romulans despite Picard's instance, and the planet was annihilated, just like in Abrams' movie.
Though Star Trek: Picard doesn't mention the Spock connection, the destruction of Romulus looms large in the new series. It's clear in the first episode that the Federation's relationship with the surviving Romulans is going to be a major part of the show--but we'll have to wait and see how that relationship develops.
