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This is true not only because so much happens to him in such a short time, but also because plenty is still unknown about what Obi-Wan and Anakin did between Star Wars: Episode I - The Phantom Menace and Star Wars: Episode II - Attack of the Clones. Nevertheless, The Phantom Menace, Attack of the Clones, Star Wars: Episode III - Revenge of the Sith, and even Star Wars: The Clone Wars have provided plenty of insight into the biggest moments in Anakin's life. One moment in particular was the true start of Anakin's fall to the dark side.
Anakin's Separation From His Mother Was The Start Of His Troubles
Anakin Wanted To Become A Jedi, But This Sudden Change Was Jarring
In The Phantom Menace, Anakin was introduced not as an angry teenager or even a powerful Jedi but as a young boy living in slavery with his mother on Tatooine. At first, it was difficult to imagine how this kind-hearted child who wanted to help Qui-Gon Jinn, Pé, and Jar Jar Binks get to safety and built a droid to help his mother could turn into one of Star Wars' most powerful Sith. The answer became clear quickly after Anakin left his mother and went to the Jedi Temple with Qui-Gon.
It was immediately clear that this separation was going to be difficult for Anakin. When he started to walk away from his mother and his home, he ended up running back to her, telling her he couldn't do it. Even when Shmi convinced him to go and not look back, once on the ship, Anakin expressed that he was cold and missed his mother. Eventually, these sentiments would be repeated back to him by the Jedi Council.
Unfortunately, unlike Pé, the Jedi were not all that comionate in response. Rather, they made Anakin feel as though he was doing something wrong, even as he was entirely unfamiliar with the ways of the Jedi and had never been away from his mother before (meaning, his feelings were entirely natural). This initial separation from his mother and feelings of rejection from the Jedi were not the true beginning of Anakin's turn to the dark side, but they certainly laid the foundation.
This initial separation from his mother and feelings of rejection from the Jedi were not the true beginning of Anakin's turn to the dark side, but they certainly laid the foundation.
Anakin's Time With Pé On Naboo Sealed His Fate
It Was On Naboo That Anakin And Pé Were Able To Explore Their Feelings
10 years after leaving his mother (and Pé), Anakin had another encounter with Pé, under equally dire circumstances. In this case, someone was after Pé, and Anakin and Obi-Wan were called upon to protect her. This led to the absolutely bewildering decision by the Jedi to send Pé and Anakin off to Naboo together, essentially giving them a romantic retreat on a beautiful planet, even if that was inadvertent.

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This, too, was not the singular event that kicked off Anakin's turn to the dark side, although it made him so much more susceptible to all that was coming—Palpatine's manipulations in particular. Despite Anakin and Pé directly discussing that a secret relationship would be their downfall, the two became increasingly affectionate and romantic with one another on Naboo. Ultimately, this led to their return to the planet and their marriage. It was this exact relationship that would eventually be the tipping point for Anakin, although something much more sinister was the true beginning of his fall.
The Tusken Raider Incident Was The True Beginning Of Anakin's Dark Side Path
This Was The Defining Moment In Anakin's Fall To The Dark Side
The true beginning of Anakin's path to the dark side was his massacre of the Tusken Raiders. Prior to this brutal slaughter, there had been a number of warning signs, and it's clear that Anakin wasn't a perfect Jedi. He was egotistical, he struggled to keep his anger in check, and, obviously, he had an attachment to Pé (and still to his mother as well). While these were flaws that needed to be worked out, though, Anakin had yet to truly do something evil—that only began with his attack on and murder of the Tusken Raider men, women, and children.
Often, a fall to the dark side is not a singular moment but rather a slow burn. This was certainly true for Anakin. This massacre was the beginning, but it wasn't until Revenge of the Sith that Anakin fully and truly embraced the dark side. However, this event is essentially a straight line to the events of that movie. Because Anakin had experienced nightmares about his mother's death and ignored them, when he began having nightmares about Pé dying, he was desperate to act in time.
Often, a fall to the dark side is not a singular moment but rather a slow burn.
The Tusken Raider incident tapped into a newfound capacity for violence in Anakin, but it did something else too. In all likelihood, Anakin believed that, had he arrived in time and carried out that massacre sooner, his mother would have lived. Anakin may have felt that what was wrong with the Tusken Raider slaughter wasn't the violence but rather the timing. For that reason, he was willing to carry out a massacre again in Revenge of the Sith (in this case, Order 66) to save the person he loved because he hadn't done so in time the first time.
The Fear Of Losing Pé Was Too Great For Anakin To Overcome
After The Loss Of His Mother, Anakin's Nightmares Were Too Much
All of these events perfectly laid the foundation for Anakin to be tempted to the dark side. With the early separation from his mother and rejection from the Jedi, Anakin felt as though he was truly alone. Even Obi-Wan, he believed, didn't really understand him. When he then lost his mother because of his lack of action (in his mind) and betrayed his own ideals and the way of the Jedi by killing the Tusken Raiders, he believed he was irredeemable—an idea that Palpatine directly preyed upon.
This left Anakin feeling as though he only had one person in his life who was really on his side and cared about him: Pé. Given how much he had been through and how much he had caused, when Anakin said he couldn't live without Pé, he really meant it. It was only Pé, he thought, who would stand by him. This was also something Pé had proven given her muted reaction to Anakin's confession about killing the Tusken Raiders. He was therefore willing to do anything to keep her alive.
Given how much he had been through and how much he had caused, when Anakin said he couldn't live without Pé, he really meant it.
No Single Event Really Caused Anakin's Fall
In The End, This Was A Multi-Layered Issue
While the Tusken Raider incident was the beginning of Anakin's dark side path, it's also true that no one thing 'caused' Anakin's fall to the dark side. Anakin was in part a victim of his circumstances and in part influenced by those around him—Palpatine intentionally and the Jedi inadvertently. He was also, of course, responsible for his own actions, including his murder of the Tusken Raiders and his romantic relationship with Pé. There's also the question of whether this path was simply Anakin's fate, and there was nothing he could have done about it.
The truth is, it was a mix of all these factors that led to Anakin's turn to the dark side. Because of these influences, his experiences, and his personality, Anakin was just a flawed boy and then a young man who was angry, afraid, alone, and had no real outlet to work through these feelings. Yes, the Tusken Raider incident was the beginning of the end in of Anakin Skywalker/Darth Vader's path to the dark side, but Star Wars has proven that it was so much more than any one moment.