The Syrian theater exemplifies Russo-Iranian cooperation, but there are other theaters in which Moscow and Tehran have cooperated for years. Their partnership in the South Caucasus and the energy-rich Caspian Sea area are examples of this trend. Taken together, these instances of Russo-Iranian cooperation fit into the pattern of “geopolitical chaos” across Eurasia in which Moscow and Tehran, as well as other regional powers, work together to challenge US dominance.