when did azerbaijan gain independence

Azerbaijan first declared its independence on May 28, 1918, establishing the Azerbaijan Democratic Republic, which was the first modern republic in the Islamic world. This republic lasted only 23 months before Soviet forces invaded in April 1920. Azerbaijan regained its independence from the Soviet Union later, with the Parliament adopting the Constitutional Act "On the State Independence of the Republic of Azerbaijan" on October 18, 1991. This act declared Azerbaijan an independent sovereign state. A nationwide referendum in December 1991 affirmed this independence. October 18 is celebrated as Azerbaijan's Independence Day, marking the country's exit from the USSR.