"Endgame angst" (September 16th) overstated the significance of a supposed land route for Iran running from Tehran through Syria to the Mediterranean. It has always been easier and less dangerous for Iran to supply weapons to Hizbullah by air. A land route is much longer and vulnerable to insurgent attacks. Iranian convoys transporting militiamen and weapons by land would present ideal targets for Islamic State, for example.
In reality, the main driver of the eastern campaign in Syria is the Syrian regime itself, which wants to reopen trade routes with Iraq and regain control of the country's most valuable oilfields in order to secure reconstruction prospects and thus a more viable economic and political future. For instance, the regime would have a much weaker hand if the Kurdish-dominated Syrian Democratic Forces had control of those fields.
In this light, the Iranians are merely helping a vital ally. One can justifiably criticise the Iranians' methods, but this explanation is far more convincing than the narrative of securing a land route from Tehran to the Mediterranean.