9 September 19911991
Tajikistan's declaration of independence from the Soviet Union.

On September 9, 1991, the Republic of Tajikistan officially declared its independence, seceding from the Soviet Union.
Although this event did not occur directly within Iran's borders, it holds a special place in Iran's regional calendar due to the linguistic, cultural, and historical ties between Iran and Tajikistan.
Tajikistan currently shares borders with Kyrgyzstan, Uzbekistan, Afghanistan, and China.