Georgians () are an indigenous Caucasian nation and ethnic group. Georgians constitute a majority of the population in Georgia. Large Georgian communities are also present throughout Russia, the Post-Soviet states, Iran, United States and to a smaller extent, the European Union. The majority of Georgians are Eastern Orthodox Christian and most follow the national autocephalous Georgian Orthodox Church, which originated in the 4th century. There are also Georgian Catholic and Muslim communities in Tbilisi and Adjara. A complex process of nation formation has resulted in a diverse set of geographic subgroups, each with its characteristic traditions, manners, dialects and, in the case of Svans and Mingrelians, language. The Georgian language, with its own unique writing system and extensive written tradition going back to the 5th century, is the official language of Georgia as well as the language of literacy and education of all Georgians living in the country. Georgian, Svan and Mingrelian, together with Laz spoken by the related Laz people form the Kartvelian language family. Located in Caucasia at the border of the southeastern edge of Europe, the Georgian people have fought to protect their Christian identity in the face of immense pressure from the neighboring Muslim empires. By the early 11th century they formed a unified kingdom which emerged as a dominant regional power until it was weakened by the invasions of the Turco-Mongol conqueror Timur and by internal divisions following the death of George V the Brilliant, the last of the great kings of Georgia. To ensure its survival as a Christian kingdom being threatened for centuries by their Safavid, Afsharid, and Qajar Persian suzerains, the eastern-Georgian kingdom of Kartli-Kakheti, being the most dominant Georgian power at that time, led by Heraclius II found itself able to abjure any dependence on Persia or any other power by signing the Treaty of Georgievsk in 1783, and by this forged an alliance with the Russian Empire, which was viewed as a replacement for the fallen Byzantine Empire, Georgia’s traditional ally. Eventually being annexed by Russia in 1801, the Georgians briefly regained national independence from 1918 to 1921, and finally, in 1991 from the Soviet Union.