By changing his past, Barry alters the timeline, resulting in "Flashpoint"
Though he is somewhat able to restore the timeline, this creates new threats, including Savitar

After Harry and Jesse return to Earth-2, another Wells doppelgänger is recruited: the novelist "H.R." Wells
Both Wally and Caitlin Snow begin to manifest metahuman abilities; Wally suits up as the speedster Kid Flash

While Caitlin is forced to suppress her ice-powers to prevent becoming Killer Frost
When Barry accidentally travels to the future and sees Iris killed by Savitar, he is desperate to change the future to prevent that from happening
After saving Iris and defeating Savitar, Barry takes his place in the Speed Force