<font color="red"> Who would invade us?</font>

Given the current state of the world, this is undeterminable. In 1925, if you asked England "who would ever invade you", and the answer was "Im not sure", is that sufficient reasoning to assume no one will ever invade England?

<font color="green"> Why would they do it? </font>

To topple our government, take control of our natural resources, take control of our strategic position, take our land, control our waterways...I could go on, but the answer lies in the overwhelmingly immense history of stronger countries invading weaker countries, even in the absence of any feasibility to success. Why do any stronger nations ever invade weaker nations?

<font color="orange"> How would they do it? </font>

That would give away the answer to my not so secret and relatively widely understood riddle.