What did the planes have in common? they were all domestic flights heading towards the West coast, which means that they would have a great amount of fuel on them: this would increase the explosion and fire after the crashes. This was a likely reason for those and not other planes being chosen.
Winston Churchill was not worried about America since he knew they had strong industrial power
Nobody chooses the rulers. If its through a system of heredity, when the rulers die their children take over.