Captain America: The Winter Soldier introduced political thrillers and espionage to the Marvel Cinematic Universe. Meanwhile, Captain Marvel introduced the Skrull race and their decades-long struggle to find a home. Secret Invasion became the perfect meld of both properties as it asked what would happen when a group of disgruntled Skrulls chose to fight back. Infiltrating high-profile positions by assuming the identities of individuals like Rhodey to take over from within, these Skrulls planned to end humanity and rule.
Source：https://www.cbr.com/secret-invasion-explain-why-skrulls-remained-human/
