They are calculated risks, every possible scenario is gone over many times before they make such a commitment. There are some they hope will not happen and others happen just as they planned. The US doesn't want to attack Iran, but they will defend an ally. None of the current wars were mistakes, either way they would of happened at some point. If it wasn't for the wars, the US economy would be much worse than it is now, every bullet, bomb, missile, uniform, medical supply, tank, etc. has millions of americans working jobs to keep the war effort moving. Basic economics, war is good for the economy.