The Caspian Sea, which is the largest lake in the world, with no natural waterway to the world's open seas, with a length of 1200 km and an average width of 300 km in the east of the Caucasus, has been the source of civilization and tribes since 75, 000 thousand years ago. In the years before the collapse of the Soviet Union, the Caspian Sea was known as a common sea between Iran and the Soviet Union, and this de facto border was recognized until the collapse. Iran, with the exception of its own issues, did not play a role in the issues of the region. The Caspian Basin was the sphere of Soviet influence, and the Soviet Union dominated the northern, northeastern and western parts of the region as part of its territory. Following the collapse of the Soviet Union in 1991, a couple of countries were established in the Caspian region, while these states along with the great powers faced new challenges. The post-1991 Caspian Sea geopolitical region also emerged as an active and functional area. The most important issues that have changed the political geography and boundaries of the Caspian region are including: the Caspian Sea legal regime, ethnic conflicts in the countries of the region, regional energy resources as well as environmental issues. What is considered more important for Western powers is a strategic influence in a region that is considered a kind of "backyard" of Russia.