We knew Thor had received a power upgrade in Thor: Ragnarok after losing Mjolnir (his hammer) to his half-sister Hela and realising that the strength was inside him all along. But it was in Avengers: Infinity War we saw why he is called a god.
Sure, the God of Thunder got a beating by the hands of Thanos in the beginning, but we did not know how he was captured. Maybe he was outnumbered by the Black Order. And after he forged himself a new weapon, Stormbreaker (a battle axe) with the help of Eitri, he became even more powerful.
He turned the course of the Battle of Wakanda, in which the Avengers and their allies were on the verge of being overwhelmed, immediately after his arrival, destroying outriders by the scores and saving his comrades.
Even Thanos, with the power of all the six Infinity Stones in his hand, was unable to stop Thor and Stormbreaker. The weapon buried itself into Thanos’ chest. The Mad Titan was successful in snapping his fingers, but it was still a humongous achievement on Thor’s part.
But as it turns out, it was not just Thor’s strength. After all, no weapon in existence should be able to stop the combined power of the Infinity Stones, no matter how powerful the wielder is.
Turns out, Thanos was taken unawares. He had just incapacitated all the heroes who tried to stop him. And did not see Thor — or Stormbreaker — coming. Or he could have just changed reality and turned Thor into a puddle of water. That’s not to say Thor is weaker than him.
Probably he could take down Thanos sans the Infinity Gauntlet particularly with Stormbreaker. But with the power of the entire universe (the Infinity Stones are six singularities that contain the essence of the universe) in Thanos’ hands? Even cosmic entities like Galactus would hesitate.