Star Trek: Discovery has been providing some more information about the Temporal Wars in its 3rd season, and the latest hint dropped suggests that the storyline has been going on in the background of the franchise all along. The Temporal Wars were first introduced in Star Trek: Enterprise and were fought amongst a number of different species time-traveling capabilities, all of whom wished to manipulate the timeline for their own gain. They were opposed by temporal agents from the 31st century who strove to keep the timeline intact.
Star Trek: Discovery season 3 has made references to Starfleet's involvement in the Temporal Wars several times. It seems that the Federation became involved with the Temporal Wars in the 30th century, and after the conflict had ended The Federation outlawed time-travel technology. Now that Discovery is in the 32nd century, they have access to all the information Starfleet has on the Temporal Wars. Discovery's Doctor Culber made use of this information in season 3, episode 9 while attempting to figure out the cause of the illness Emperor Georgiou has been suffering from ever since episode 5. With the help of Kovich, an enigmatic Starfleet agent, Dr. Culber learned that Georgiou is experiencing molecular collapse as the result of both time traveling and crossing over from the Mirror Universe.
Kovich showed Culber the file of a Starfleet officer named Yor who experienced something similar to explain Georgiou's symptoms and revealed that Yor was a Time Soldier from the 24th century who traveled ahead in time and also across from the Kelvin Timeline, the parallel universe created by the Romulan mining ship Narada. The Narada's creation of the Kelvin Timeline was depicted in JJ Abram's Star Trek (2009) film. Besides finally confirming that Abram's Star Trek film series is canon, Yor's existence is highly interesting for another reason: in the holographic recreation of him that Kovich shows Culber, he is wearing the uniform design from Star Trek: The Next Generation seasons 1 and 2.
Yor's appearance in this uniform implies that the Temporal Wars were happening without the audience's awareness during eras of the franchise besides the time period in which Star Trek: Enterprise is set. Kovich stated that Yor traveled forward from 2379, but by that time the uniform he is wearing had been phased out by Starfleet in favor of some newer designs. Because Yor was a Time Soldier, his uniform more than likely indicates that he was sent to infiltrate the 2350s-2360s, the time period in which the uniform design was the most popular in Starfleet. The first two seasons of Star Trek: The Next Generation are set within this time period, so it's possible Yor could even have been part of an undepicted mission involving the Enterprise-D at some point. Of course, since Yor is from an alternate reality, it is possible that Starfleet used the uniform design longer in the Kelvin timeline than they did in the Prime timeline, and the holographic depiction of him is accurate to what he was wearing when he crossed over. Because Yor is only used as a brief example to explain Georgiou's condition, the episode gives little to no indication about what his uniform means, but the idea that Yor and agents like him could have been quietly going about their business in the background of other Star Trek shows is certainly a tantalizing one.
Star Trek: Discovery has been using its 3rd season to connect the show to the wider Star Trek universe as much as possible, bringing together threads from a myriad of different shows and movies throughout the franchise. These callbacks have made the show's 3rd season especially exciting for fans to watch and cemented its place within Star Trek canon. The expansion of the Temporal Wars storyline and Yor's inclusion specifically is just one example of this, but one that potentially has implications for the whole franchise. If Star Trek: Discovery is planning to do more with the Temporal Wars, it would be interesting to see Yor explored further at some point during the show.