Star Trek Discovery: Every Easter Egg & Hidden Reference From 'That Hope Is You'
3. Temporal (Hot) War
Book tells Michael that all time travel technology was destroyed and outlawed after the Temporal Wars. This could just be a throwaway line or an elaboration on Star Trek: Enterprise's Temporal Cold War, a conflict that was fought across time and space.
In Enterprise, one of the cold warriors was "Daniels", a time traveling agent of the Federation from the 31st century... not far off from the 32nd century setting of "That Hope is You".
The Temporal Cold War remains one of the franchise's most notorious dropped storylines, but it's entirely possible that the conflict escalated into an all out war (or wars) which could have major ramifications for the Star Trek Universe.