The answer to why Thanos waited until Avengers: Infinity War to steal the six Infinity Stones has finally been revealed by the filmmakers in the commentary accompanying the film's home video release. Thanos' quest for the Infinity Stones was shown nearly in its entirety in the third Avengers film, and he was ultimately successful in his plan to wipe out half of all life in the Marvel Cinematic Universe. Only his decimation of the planet Xandar happened off-screen; otherwise, fans witnessed the Great Titan take the other five Stones from their guardians, including Loki, the Collector, the Red Skull, Doctor Strange, and Vision.

However, the lingering question fans have harbored for years was: Why did Thanos wait as long as he did to assemble the Infinity Gauntlet? After all, the purple conqueror was first glimpsed in the end-credits scene of The Avengers in 2012 - after he gave Loki a scepter with the Mind Stone attached. In Guardians of the Galaxy two years later, he charged Ronan with procuring the Power Stone for him, to no avail. Finally, the end-credits scene of Avengers: Age of Ultron showed Thanos donning the Stones-less Infinity Gauntlet, promising that "I'll do it myself." Yet he didn't make any effort to do so until Infinity War. Some fans speculated that the Titan waited until various powerful deities in the universe died, like Ego in Guardians of the Galaxy Vol. 2 and Odin in Thor: Ragnarok. This would clear the field of resistance to his diabolical plan.

It turns out some of that speculation was indeed headed in the right direction. In their lively and informative commentary, directors Joe and Anthony Russo, along with screenwriters Stephen McFeely and Christopher Markus discuss Thanos' motivations and finally answer the question of why Thanos waited until Infinity War to finally pull the trigger and capture the six ancient ingots of power:

Stephen McFeely: "The catalyst for the whole movie was when Thanos... captured Nebula on his ship and rooted around in her brain and found out Gamora knew where the Soul Stone was."

Joe Russo: "It's the reason why he has not..."

McFeely: "Why he hasn't gone after it before."

Russo: "...Because the minute he does, the forces of the universe are gonna line up against him. If he doesn't know where the Soul Stone is, then what is the point?"


From the filmmakers' rationale of Thanos' methods, everything hinged on his ability to capture all six Infinity Stones, with the hidden Soul Stone essentially being the dealbreaker. Thanos needed the complete Infinity Gauntlet in order to carry through on his genocidal plan, and even having most of the Stones wouldn't allow him to wipe out half of the universe with a snap of his fingers. Therefore, Thanos bided his time especially when it came to finding the missing Soul Stone - a task he entrusted to Gamora, who later lied to him that she never found out where it was. But the mistake Gamora made was trusting Nebula with the truth that she did know the Soul Stone's secret location. When Nebula declined joining the Guardians in Vol. 2 to seek revenge on their adoptive father, she fell right into Thanos' hands - and ultimately, so did the Soul Stone.

Furthermore, Thanos, a being "cursed with knowledge," had studied Earth's heroes (including Tony Stark) and knew they would assemble to try to stop him. The Mad Titan already watched Loki fail to lead the Chitauri forces to conquer Earth, and he also saw Ronan destroyed by the ragtag group called the Guardians of the Galaxy, which counted his favorite daughter Gamora among their ranks. Thanos knew exactly who he was up against and what they could do. Even his Black Order is too weak to defeat those heroes without all of the Infinity Stones. In the end, Thanos won because he played the MCU like a master chess player. The question going into Avengers 4 is whether a permanently damaged Infinity Gauntlet and an injured Thanos will be powerful enough to beat the Avengers a second time.