X-Men: Days of Future Past

Wolverine is sent back to 1973 because Kitty Pryde projects his consciousness into his younger body to prevent Mystique from assassinating Bolivar Trask. If Mystique kills Trask, she will be captured and her DNA will be used to create Sentinels that can adapt to any mutant's powers, leading to the apocalypse in the future. Wolverine must convince the young Xavier and Magneto to work together to stop her.

The opening scene in the dystopian future shows the desperate situation the mutants face, establishing why changing the past is their only hope.

Mystique wants to kill Bolivar Trask because he is the architect of the Sentinel program, a covert initiative to develop robots designed specifically to hunt and eliminate mutants. Trask has been capturing mutants for experimentation and plans to convince world leaders at the Paris Peace Accords to approve his Sentinel program, which would lead to the mass extermination of mutantkind.

Mystique's earlier intervention in Saigon, where she stops William Stryker from capturing mutant soldiers for Trask's experiments, reveals her personal vendetta against his work.

If Mystique assassinates Trask in 1973, she gets captured rather than killed. Trask's company then extracts her DNA and uses it to engineer Sentinels capable of adapting to any mutant's powers. This makes the Sentinels nearly unstoppable, because they can counter any defensive mutation they encounter. Her shape-shifting abilities become the template for the very weapons designed to exterminate mutants.

The future Sentinels' ability to adapt is shown in the opening Moscow attack, demonstrating why the past must be changed.

Magneto is imprisoned under accusations of assassinating President John F. Kennedy, which is a twist on the real-world "magic bullet theory" from the Warren Commission report. The film suggests Magneto was framed for JFK's murder, though the exact circumstances are left ambiguous. This false imprisonment keeps him locked away during the critical period when the Sentinel program could have been prevented.

The reference to the JFK assassination is planted early when Magneto is mentioned as being held in the Pentagon prison.

Professor Xavier stops using his serum because he realizes that suppressing his telepathic abilities is preventing him from guiding Mystique away from violence. The serum allows him to walk but also blocks his mental powers, which he needs to communicate with and persuade Mystique during the White House confrontation. By abandoning the serum, he sacrifices his ability to walk but regains his full telepathic strength, enabling him to talk Mystique out of assassinating Nixon.

Xavier's struggle with the serum is established early, showing his dependence on it to walk.

Magneto attempts to kill Mystique in Paris because he believes that eliminating her will prevent her DNA from being harvested by Trask's company. If Mystique dies, Trask cannot use her shape-shifting genes to create adaptive Sentinels. However, this plan backfires because it triggers the public revelation of mutants when Magneto uses his powers, which shocks the world and ultimately leads Nixon to approve the Sentinel program.

The tension between Magneto's willingness to kill one mutant to save millions is established through his conversations with Xavier.

After the confrontation in Paris, mutants are revealed to the public when Magneto uses his powers to attack the crowd and try to kill Mystique. This shocking display of mutant abilities causes President Nixon to fear mutant threats and grants approval for Trask's Sentinel program. The very event meant to prevent the Sentinel program inadvertently triggers its creation.

The chaos in Paris is designed to stop Mystique but instead creates the public panic needed for the program to pass.

Mystique spares Trask because Professor Xavier uses his telepathic powers to communicate with her and convince her that killing will only make things worse. He persuades her that choosing mercy, rather than assassination, will change public perception of mutants. After Xavier's intervention, Mystique disguises herself as Nixon, stops Magneto's Sentinel attack, and allows Trask to be arrested for treason instead of killing him.

Xavier's earlier decision to stop using his serum directly enables this telepathic persuasion.

When Mystique spares Trask and he is arrested for treason, the Sentinel program is cancelled before it can begin. This prevents the creation of adaptive Sentinels, fundamentally altering the future. The dystopian timeline is erased, and Wolverine wakes up in a reformed present where characters who previously died, including Jean Grey and Cyclops, are now alive. The X-Men are united, and mutants live in a more peaceful world.

The altered future is glimpsed briefly as Wolverine transitions back, showing changes in the environment.

At the end of the movie, Mystique impersonates William Stryker to infiltrate and extract Wolverine from whatever facility he was being held in. This shows that despite the timeline change, Stryker still exists as a threat to mutants, and Mystique continues her work protecting mutantkind through shape-shifting and infiltration.

Stryker's earlier appearance in Saigon, where he attempts to capture mutant soldiers, establishes him as an ongoing antagonist.

Kitty Pryde's ability to project consciousness into the past requires significant mental energy. The longer she maintains the connection, the more it drains her. When the Sentinels attack the sanctuary in China and get closer to finding the mutants, Kitty must concentrate harder to keep the temporal link open while also protecting the team. This nearly kills her when Logan's consciousness is suddenly pulled back during the battle.

The opening Moscow attack shows Kitty struggling to maintain the time projection while under Sentinel assault.

The young Professor Xavier in 1973 relies on a serum because he was severely injured during the Cuban Missile Crisis, as shown in the previous X-Men films. The serum allows him to walk but also suppresses his telepathic abilities, which is why he appears less powerful than his older self. The X-Mansion has also closed down due to the Vietnam War draining its staff and students.

Xavier's dependence on the serum is revealed immediately when Wolverine meets him in 1973.