system
Given the following post, respond as if you're commenting on Reddit:
human
[MCU] Why were terrans basically the only people fighting Thanos?

Sure Thanos decimated Xandar, but destroying half of all life is somewhat of a universal problem. Why didn't planets get together and hunt him down before the stones were taken? Even if they didn't know his specific plans they knew he was hunting for the extremely dangerous weapons.

It seems like both stands against him were raged on Earth without much assistance. Couldn't the Guardians have petitioned an army from an alien species, or shouldn't some army have just gone without request - given what was at stake? Why, in the entire universe, were only like, 30 people trying to actively stop him?
gpt
First off, nobody knew his true plans. Second, people were fighting back against him, and losing. Third, when he launched his quest for the Infinity Stones proper, it was a blitz operation conducted only when he knew he could get all six in a matter of days - far too quickly for anyone to effectively rally an opposition against him.