In the event America was invaded by another country?

The coast lines. Alaska because of its' proximity to Asia. Texas because of shared boarder with Central and South America. D.C. as it is the capital, Manhattan, pretty much all of New York. Interior cities would be important if a beach head was established.

A new study, which ranks cities by their vulnerability to terrorism, identified Boise, Idaho, as the most assailable city by terrorists in the Western United States, reports the Los Angeles Times.

Boise came in 10th place behind the top five most vulnerable cities: New Yok City-Newark; New Orleans, Louisiana; Baton Rouge, Louisiana; Norfolk, Virginia; and Charleston, South Carolina—all port cities.

Port cities and manufacturing cities off the top of my head, but it would be important to defend cities where any kind of military base is located as well.

Le Mars, Iowa. It's where they make Blue Bunny Chocolate Lovers Ice Cream Cones.

None. Mountain passe's. river bridges, choke points, it is a long walk city to city with every culvert and bridge gone creeks to wade rivers to swim mountains to climb. And some city's we could give them. Hungry population behind them stealing them blind.

Lol that isn't happening. But if it did, it would be just get rid of them and protect everything rather then one city

Makes no difference. I may not die for my government, but I will die for my people! There is a big difference! People still have to realize this!

The Capitol (For obvious reasons) and Norfolk (Crucial military area).

DC, coastline, and the big cities like NYC and LA because our military would do something like that for no reason :p

NSA headquarters and CIA headquarters...dr