Warning: This Post Contains Spoilers!
Thanks to the developments of Marvel Cinematic Universe, Thor and Asgard have become pivotal players in Thanos' quest to obtain the power of Infinity Stones for himself. Not only are the Asgardians aware of the threat that stones present to the universe, they're also in possession of a key Infinity Stone that Thanos needs.
Read on below to find out how the events of Thor: Ragnarok allow Thanos to get his hands on the Infinity Stone hidden inside The Tesseract:
How Thanos Gets The Space Stone
After Loki's failed attack on NYC in The Avengers, Thor took The Tesseract and Loki back to Asgard where they could be locked away (respectively). The Tesseract has remained in Odin's Vault ever since, holding a very important secret inside its cubed structure: it's actually the Space Infinity Stone.
At the end of Thor: Ragnarok, Thor and Loki realize that the only way to stop Hela from slaughtering every Asgardian is to restore Surtur the fire demon to full power, and let him unleash Ragnarok upon Asgard. While Thor battles Hela, Loki must infiltrate Odin's to retrieve the artifacts that will restore Surtur's power; however, while completing his task, Loki can't help but notice that the Tesseract is all his for the taking.
In Thor: Ragnarok's mid-credits scene, Thor, Loki, and the surviving Asgardians are traveling through space on a ship, trying to establish a new Asgard on Earth, after Surtur has destroyed their previous homeland. While on their travels, the Asgardians' ship is intercepted by a much larger vessel, which Marvel Studios head Kevin Feige confirms belongs to Thanos, and is named "Sanctuary II."
The dots are easy to connect: Thanos intercepts Thor and Loki's ship in order to make Loki repay his Avengers failure, and Loki offers up The Tesseract as that payment. That development has already been confirmed by a scene of Loki on bended knee, offering Thanos the Tesseract, in the Avengers: Infinity War SDCC trailer.
Why He Wants It
It makes sense that Thanos would seek out the Tesseract Infinity Stone as one of his first targets; the power of the Space Stone allowed Loki to bring a Chitauri armada to Earth - so it can presumably transport Thanos and his minions all over the cosmos, to attack every location where other Infinity Stones are being kept with little to no sign that they're coming.
No doubt, the heroes of the Marvel Cinematic Universe will be facing just that kind of surprise assault from Thanos and his Black Order, in the opening act of Avengers: Infinity War.
Thor: Ragnarok is in theaters. Other upcoming MCU movies include Black Panther on February 16, 2018, 2017, Avengers: Infinity War on May 4, 2018, Ant-Man and the Wasp on July 6, 2018, Captain Marvel on March 8, 2019, the fourth Avengers movie on May 3, 2019, the sequel to Spider-Man: Homecoming on July 5, 2019, and Guardians of the Galaxy Vol. 3 in 2020.