WARNING: This Post Contains Spoilers!
Thor: Ragnarok is the last Marvel Cosmic movie fans will get before intergalactic threat of Thanos looms over the entire Marvel Cinematic Universe in Avengers: Infinity War next summer. As such, Thor 3 had a fair amount of stage-setting for Infinity War, with some small but crucial developments.
Read on below for a breakdown of how Thor: Ragnarok sets up Thanos for universal conquering in Avengers: Infinity War!
The first major development in Thor: Ragnarok that's going to have a significant effect on Avengers: Infinity War is no doubt the Death of Odin (Anthony Hopkins) and fall of Asgard.
Until this point, the MCU Asgardians have been a major peacekeeping force in the universe, with Odin being the head sheriff. Thor: Ragnarok already showed us how a universe without Odin opens doors to new threats - and Thanos making a play for the Infinity Stones is something the All-Father would've likely intervened in.
But with Odin gone, and just one small band of Asgardians now wandering the stars, Thanos has a perfect window of opportunity to make his move.
As Marvel fans know well by now, The Cosmic Cube or "Tesseract" (which was the major MacGuffin of both Captain: America: The First Avenger and The Avengers) is actually the Space Infinity Stone. There was a big question of how Thor: Ragnarok would get the Space Stone from where it was locked in Odin's vault to where it will inevitably end up mounted on Thanos' Infinity Guantlet - and now we know!
In the final battle against Hela, Thor and Loki hatch a scheme to restore the fire demon king Surtur to full power, in order to bring Ragnarok down on Asgard, and Hela. In order to pull that off, Loki must infiltrate Odin's vault and put The Crown of Surtur into the Eternal Flame; but while accomplishing his task Loki can't keep his eye off of another prize in Odin's Vault: The Tesseract.
While Loki's theft is not explicitly shown, it's pretty clearly implicated in Thor: Ranarok's mid-credits scene. During that button scene, we see Loki and Thor aboard the 'lifeboat' spaceship carrying the last Asgardians, when their ship is dwarfed by a much larger and ominous-looking vessel. As Marvel's Kevin Feige has revealed, that ship is Thanos' 'Sanctuary II' vessel.
With Thanos about to presumably take possession of the Space Stone, The Mad Titan will be able to use its power to move across the universe on a whim, or transport his forces wherever they may need to travel, or invade. In short: this is how Thanos and his Black Order lieutenants will be able to launch surprise attacks on multiple fronts, when Avengers: Infinity War begins.
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.