Don Karnage needs to get a copy of Einstein's research. Any other person who is not air pirate could help Karnage enter the city or do some real damage on their own.

I couldn't have said it better, KitCloudkicker52885.

Since no one seems to be answering, I guess I'll give it a try.

If you look at the city from Kit's first visit of Cape Suzette in Plunder & Lightning, you'll see that the gap in the cliff is basically the only way in and out via planes and boats. Of course, planes can go other ways if they fly high enough. As you will see in dozens of episodes, the cannons (cliff guns, Baloo called them) are pretty effective against attacks like the Air Pirates and the Iron Vulture.

"For years, I have tried to visit your fair city, BUT YOU HAVE ALWAYS SHOOTED AT ME!" -Don Karnage

Apparently, their deference worked well against them for years until Don Karnage got a Lightning Gun. The cliff guns kept them at bay, and even if they got pass the guns, they have whole fleet of planes armed with guns as backup.

Yes, in light of World War II and our modern war machines, we can see flaws in Cape Suzette's one-way entrance, a cliff loaded with guns. One Atomic Bomb or a less powerful weapon can reduce the cliff to nothing. But, Cape Suzette is lucky, the Air Pirates are too dumb to get through without disguising themselves as citizens, and they no longer have a powerful weapon to break through anymore.

But do remember, this is a cartoon, reality doesn't have to influence it. They can be very safe inside their armed cliff wall, believing that they are safe from Pirate attacks and that would be enough.

If Darkwing Duck had to come face to face with our reality instead of cartoon reality, he'd be a roasted duck years ago. In other words, don't go too deep into a cartoon's logic and reality and comparing it with ours. They are only made to amuse and entertain us.