Since adopting a democratic constitution in 1991, the sovereign state has been a unitaryparliamentary republic with a high degree of political, administrative, and economic centralisation. The population of seven million lives mainly in Sofia and the capital cities of the 27 provinces. The population has declined since the late 1980s.
The name Bulgaria is derived from the Bulgars, a tribe of Turkic origin that founded the country. Their name is not completely understood and is difficult to trace back earlier than the 4th century AD, but it is possibly derived from the Proto-Turkic word bulģha ("to mix", "shake", "stir") and its derivative bulgak ("revolt", "disorder"). The meaning may be further extended to "rebel", "incite" or "produce a state of disorder", and so, in the derivative, the "disturbers". Ethnic groups in Inner Asia with phonologically similar names were frequently described in similar terms: during the 4th century, the Buluoji, a component of the "Five Barbarian" groups in Ancient China, were portrayed as both a "mixed race" and "troublemakers".