A surprise attack using commercial planes which are always flying around the US. Very different from a surprise invasion. An invasion is a massive logistical exercise, using resources that don't look civilain. It also cannot be done solely, or even mostly, via the air, it'd take a massive navy, and the US also has one of those.TheEndlessSleep said:Historically, the USA used to be fairly complacent in times of peace and lax in terms of its own security.
For example, before the state of fear that we currently live in, the USA was so confident of its own superiority that throughout the 1990s its defences were surprisingly thin.
9/11 for example...
On the 11th September 2001, guess how many fighter jets were on station to protect the US mainland... 500, 1000, 20000?
No, 14, and only 6 were on the Eastern seaboard, and the closest pair of them to NY were 150 miles away! At the point of the impact of the first tower, the jets had been in the air for 20 minutes, but were still 50 miles out.
I guess what I'm saying is that it is possible that at one point a surprise invasion like this would have been sucessful.
However, I think you are right that nowadays it is fairly impossible. The USA has learned what happens when they let their guard down, and they're not likely to allow it to happen again.
Also, isn't part of the backstory that the US withdrew its overseas forces, so there would be much more defending the contiguous United States.
And then, the US still has it's powerful second strike capability, such as a SSBN fleet lurking somewhere in the oceans of the world.