Norman Podhoretz writes in the current issue of Commentary that failure to attack Iran militarily and end its nuclear program is tantamount to Neville Chamberlain's appeasement of Nazi Germany with the Munich agreement of 1938.
But the historical parallel is less than perfect. Having united Austria with Germany, Hitler made preparations to invade the Sudetenland of Czechoslovakia, which bordered on Germany. A short-sighted Chamberlain immediately sat down with Hitler in an attempt to prevent a military conflict.
Chamberlain got a promise from Hitler that Germany would refrain from an invasion of Czechoslovakia in exchange for Britain's and France's agreement that the Sudetenland would go to Germany. Nevertheless, both Germany and the allies used the appeasement to prepare for war. Hitler reneged on the agreement a year later and invaded Czechoslovakia as well as Poland.
In the present case, nothing has been conceded to Iran; there are no gullible gestures of friendship from any quarter. Nothing, not even a sliver of territory has been given to Iran in return for peace. The western allies are playing a much tougher game than Chamberlain ever did with Germany. They have placed sanctions on Iran and subjected it to continual nuclear inspections whereas the allied approach to Germany was a gesture of guarded friendship.
Podhoretz advocates a preventative strike against Iran, just as the allies should have launched a preventative invasion of Germany. But the geopolitical situations are completely different as well. A preventative war in Europe would have earned Britain Europe's favour in a region which had already experienced the cost of German aggression twenty years earlier. Germany didn't have the kind or degree of sympathy throughout Europe that Iran has throughout an unstable Middle East which already mistrusts the United States. Moreover, the allies in 1938 hadn't launched any foolhardy, bloody and fumbled invasions in Europe like the US invasion of Iraq.
By contrast, a preventative strike against Iran would further destabilize an already unstable Middle East and it would likely increase rather than decrease Iranian influence, while ending once and for all what little respect the US has managed to retain throughout the region.