Sexybeast said:
is that possible that Canada invades U.S someday?
I think you might have misunderstood the statement. Canada could be used as a back door into America, the Canadian-American border is the longest un-fortified border in the world, 3000+ miles and not a single point with a 10 foot high wall or men staring at each other over a white line ready to shoot each other with one phone call. A country, most likely Russia, could go over the North Pole and then move through thousands of miles of Canadian territory without ever seeing another human being, but the possiblity of this is slip, our advanced Radar lines in northern Canada would detect any planes, the ice makes it almost impossible for ships to move on the surface, and sneaking a huge fleet of submarines under the ice, and into Hudson Bay filled with troops and supplies is very unlikely.
The Navy would have to be almost completely destroyed in order for this to be accomplished, only a Russian-UK coalition could pull this off, even then it is unlikely because of the lack of new equipment and maintenace on existing Russian ships and the Royal Navy does not have a huge technological advantage on the US.
And the Air Force would have to be weakened to a great degree also. Our bombers would pose a threat to larger ships with the ability to drop nukes on the fleet (doesn't destroy all the ships but will cover the decks with radiation) and fighter-bombers like the F-22 Raptor, one of the world's most advanced, could be in and out of a fleet of ships in a matter of minutes with little or no warning.
And also the resilence of the American People, a lot of people like to say that America has no will to fight, and then they use Afganhistan and Iraq as examples. Well the US is not being invaded in either of those cases so the average person is not gonna feel the pressure of a war on one's doorstep. The US has a population of 280,00,000+, when I joined the Army I was told that only 12% of the population was eligible to join the military. If the US is invaded the draft would be enacted, so let's just say that half of those eligible are drafted into the military (we can supply the weapons and most Americans in the Mid West hunt or at the least know how to shoot.) so 6% of the population is drafted, that means we would have an Army of roughly 16,800,000, with a 7 to 1 logistics ratio that means that about 2.4 Million combat troops to fight in defense of their homes and families. How many countries could field an Army that big to invade the US? Not many. Maybe 2 million max to invade, that includes the troops needed for logistics.