With the end of sanctions on Iran, the country's regional economic influence will begin to rebound. The adjacent South Caucasus region, encompassing Azerbaijan, Georgia and Armenia, is one area that Tehran will target for greater cooperation, reaching out to make deals on trade and energy. In doing so it will inevitably have to consider the role of Russia, which has dominated the political and economic affairs between the Black and Caspian Seas for two centuries. Russia and Iran are historic geopolitical rivals, a relationship manifested in the long-simmering Nagorno-Karabakh conflict between Azerbaijan and Armenia and on negotiating pipeline projects for Iranian hydrocarbon exports. In spite of their rivalry, Russia and Iran will have to work together in order to block Western-led infrastructure projects, which they both oppose, and to avoid foreign military presence in the region, particularly by Georgia....