This book is set in the 1950s. The idea is that the Kree and the Skrull and who-ever-else has heard rumors that the Space Stone (also known as the Tesseract) is on Earth and have sent small groups of their own to discover if that’s true.
S.H.I.E.L.D. realizes that they need heroes and they need them now. This program is launched.
The alien crews decide to give up and go away. Remember this isn’t an armada or anything. This is considered a backwater assignment.
However, the Kree warrior Mar-Vell stays behind as Doctor Lawson, a doctor cleared to work on the Pegasus Project.
Discussion Link: https://www.cbr.com/strikeforce-morituri-brutal-series/