4Salt:

What you just described already happened once…I think it was called the Revolutionary War. Remember, the British thought the EXACT same way you do!!!
The rest is History..

Just a side note. The Army that you are describing that are experts in urban warfare and the best training in the world in called the US Army/Marines/Air force/Navy… Other than that I really think that with so many reservists and ex-military out there alone, can't forget the militias, the sheer size of our country, I don't think anyone would have a chance in hell!!!