SPOILERS for The First Purge ahead.
While history is littered with examples of sequels gone horribly awry, in general the concept of continuing a film's story and catching up with its characters isn't all that hard to pull off in a way that at least momentarily entertains fans of the original. Much harder to pull off successfully is the prequel film, since - in theory - viewers already know what happens afterward, and if previous characters are used, whether they'll survive the prequel or not isn't in question.
For the most part, The First Purge avoids this trap, despite being a prequel to the three prior Purge films. Outside of a rather strange continuity gaffe involving a poster for Blumhouse's 2018 Halloween sequel, very little is done to establish the film as taking place in any particular time period, and if not for the original movie spelling out when the first Purge night happened, this could theoretically be set in any year prior to the attack on the Sandin family in 2022. It also doesn't feature any characters from prior installments, making the drama surrounding the ultimate fates of its focal characters very palpable, and not at all a foregone conclusion.
The Mid-Credits Scene & The Purge's Future
After all is said and done and the first experimental Purge of Staten Island is completed, a scene pops up during the credits featuring a post-Purge press conference from evil government stooge Arlo Sabian (Patch Darragh), chief of staff to recently elected President Bracken. Bracken, of course, represents the now in power New Founding Fathers of America party which, as the film makes clear, implemented the Purge concept as a way of wiping out poor and primarily minority populations it deemed undesirable and a drain on society.
Thanks to the diabolical efforts of Sabian to artificially cause increased participation in the Purge, Sabian announces during the credits scene that the experiment has been deemed a success, and that the New Founding Fathers plan to push for a nationwide expansion of the Purge concept. As fans all know, this effort proved successful, leading to the chaotic Purge nights seen in the other films, including the death of James Sandin (Ethan Hawke), the moral journey of Leo Barnes (Frank Grillo), and the eventual election of Purge opponent Senator Charlie Roan (Elizabeth Mitchell). The scene is thus not really setup for any new film, more providing the final piece of the Purge puzzle.
After that scene, things aren't quite over yet, as a new trailer for Syfy and USA's soon to debut Purge TV series is shown as a treat for those who hang around until near the end of the credits. Interestingly, where exactly the series takes place within the franchise's timeline is unclear, as is whether characters seen in the movies will appear at some point during the show. As with The First Purge though, the series' focal characters will be all new. In an intriguing change of pace, the Purge's TV variant will be set in a smaller city, which presumably will present a different set of dangers than the ones faced by characters trying to survive the night in a sprawling metropolis.