In 1935 Adolf Hitler gambled that the French would not react when Germany moved military units into the Rhineland, an area that had been demilitarized as a result of the Versailles agreement that ended WWI.
Hitler was right, the French barely lifted a finger to stop this blatant violation of the Versailles treaty. For Hitler this was all the confirmation he needed that the West would not act to stop his aggression. Indeed, over the next few years Hitler would acquire massive amounts of territory and wealth because the West refused to confront him while he was still weak. As a result they were forced to fight him when he had grown very powerful.
In the Middle East the same power plays are unfolding before us. Iran has tested its own Rhineland and found the will of the West lacking. More acts of aggression will follow.
At some point we will have to fight Iran. Unfortunately it looks like history will repeat itself and we will wait until they have grown powerful; possibly after the have acquired nuclear weapons.
Those who cannot remember the past are condemned to repeat it. -George Santayana