Which is the worlds oldest country?

As far as I know it is Bulgaria - founded in 681 AD, when khan Asparukh and his people (presumably around 1.5 million) crossed the Danube river, invading Byzantine empire, allied with the Slavic tribes, crushed the Byzantine armies and signed a peace treaty with Byzantine empire, according to which they had the right to rule the lands north from the mountain Stara Planina and Byzantine empire had to pay tribute.