The DeCarlos gang are the Red Skulls main enemies. Furthermore the gang helps you to find Betty in Crimson Skies: High Road to Revenge. They also mention something about "The pack of donuts" as you progress through. As the gang seems to like the Hughes Bulldog plane, they started to overthink their selection when the long-lasting battles with the Red Skulls did not seem to end, as the Hughes Aviation Bulldog is technically not able to keep up with the heavy fighter Fairchild F611 Brigand.
While robbing cargo Zeppelins to fund air and ground vehicles, the DeCarlos gang is in control of multiple petrol-producing factories in the Chicago area. Other gangs and miltias show only little to no interest for the DeCarlos at first. But when the fights with the Red Skulls gang made it up on newspaper on a daily basis, the DeCarlos gang became a possible threat for the Die Spinne corporation and a possible ally for the Fortune Hunters. DeCarlos is the only self-providing pirate gang in North America, as they can fuel their planes with self-produced kerosene.