After Hitler took the desperate gamble in 1936 of sending troops into the Rhineland, in violation of this treaty, he remarked privately, "If the French had then marched into the Rhineland, we would have had to withdraw with our tails between our legs, for the military resources at our disposal would have been wholly inadequate for even a moderate resistance."
Moreover, Hitler understood that such a fiasco would have brought down the Nazi regime. He took this huge gamble precisely because he was convinced that the French did not have the guts to act. Neither did Britain -- especially after Hitler appealed to the wishful thinkers by offering a 25-year non-aggression pact.
Those who deal with the gritty life and death choices of the real world as if they were discussing abstract questions around a seminar table said that Hitler had "just gone into his own backyard." Other nations station their troops anywhere they want, inside their own borders, why not Germany?
By the time they realized why not, Hitler had devastated half the continent and had come within a hair of destroying Britain.
At the end of World War II, Winston Churchill said that never was there a war that would have been easier to prevent. The earlier that preventive action would have been taken against Hitler, the lower the cost would have been. But history, he added, showed "how counsels of prudence and restraint may become the prime agents of mortal danger."
Caution is sometimes the most dangerous policy. And this looks like one of those times today.