While Avengers: Infinity War showed how Thanos (Josh Brolin) acquired most of the Infinity Stones, we didn’t see him claim the Power Stone, which had previously been left in the care of the Nova Corps on Xandar. According to McFeely, the scene was originally written into the film, but had to be edited out of the working script for the sake of streamlining the story.
As he explained to Yahoo! Movies, “I do remember, there was a Xandar draft, and it just became unwieldy. It’s lovely to go back to a small part of Guardians of the Galaxy and explore how you get that stone, but we had to eventually economize.” So instead of seeing the Mad Titan destroy that planet, we get to hear about it secondhand. (Similarly, fans also never get to find out exactly how he snagged the Reality Stone, because the Guardians don’t arrive until after he’s collected the Aether from the Collector).