I really want Thanos to be put to bed quickly and an Earth related villain usurping the power Thanos collected being the main villain. Otherwise it seems off that all these human heroes are the only ones willing and able to defend 50% of all life. Where as them fighting to prevent an Earth orientated bad guy seems right.
I don't expect this to be the plot howoever.
Asgard was the protector of the 9 realms, and they have almost been wiped out by Hela/Surtur and Thanos.
And there was a brief mention that Xandar was wiped out I think, which was the capital of the Nova empire.
Plus of course the snap happened on Earth, because that's where the last infinity stone was. The events of infinity war happened over the course of 2 days, and as soon as Thanos had the space stone from Loki, he could teleport wherever he wants. Think about where he was - Knowhere (It looked like everyone had been wiped out), Vormir, Titan. He was only on Earth for about 5 minutes , so nobody else in the Galaxy had much chance to stop him.