Pretty much wargamed in the “Worldwar” series by Harry Turtledove, among many others. Worldwar opens at the beginning of WWII and it is Humans vs the Lizards. Excellent read.
Turtledove creates aliens whose society advances very slowly. They have near light speed ships but their weaponry is equal to early 21st Century weapons. So could a relatively small sized invasion force armed like the forces in Iraq 2 defeat an entire world armed with the weapons of 1943. But you are right. The series was a good read.