Secret Invasion proved that even though Thanos was defeated, there were still threats in the Marvel Cinematic Universe that could destroy the Earth. In the case of the Skrull invasion, the terror came from the shadows, with a rogue Skrull named Gravik using his followers to infiltrate world powers and take the place of delegates and the media. In doing so, it would sow chaos that was meant to create a world war, annihilating humanity and leaving the planet open for a Skrull takeover. Thankfully, that was stopped thanks to the intervention of Nick Fury, but it proved a larger issue with Earth.
Source：https://www.cbr.com/secret-invasion-catalyst-mcu-real-illuminati/
