Persian emerged as the common language of court life and administration in the Islamic world east of Baghdad in the 8th and 9th centuries (2nd and 3rd centuries into the Islamic era). The process began in Khurasan, the large historical region of southwest-central Asia, which besides the northeast quadrant of modern Iran included most of modern Turkmenistan, Uzbekistan, and Tajikistan, and northern Afghanistan. Persian radiated out from the pre-Islamic cities that became new power centers, filling the vacuum left by the declining political (as distinct from symbolic) role of the Caliphate in Baghdad. Persian spread to its greatest extent five centuries later, under Mongol and Turkic administrations, when it stretched from the Balkans in the west to southern India in the south and along the trade routes into central China in the east. A century later, it began to give way to the rise of vernacular languages—first in the west, where the use of Ottoman Turkish increased in the 15th century. It finally declined significantly in the east in India in the 19th century, where the British replaced it formally with Urdu and English in 1835. Over the past century and a half Persian has undergone a process of functional transformation, passing into the status of a classical language, as locally people began to write in Pashto, Sindhi, Urdu, and other vernaculars in the peripheral territories of the Islamic world. In the 20th century, at the expense of losing its unitary identity and universally standard form, Persian achieved the modern status of national language in three countries—in Afghanistan, (where it was renamed dari), in Iran (as Fārsi), and in Tajikistan (where it was renamed tajiki, or tojiki when transliterated from Cyrillic). It is still spoken widely in Pakistan, Uzbekistan, and the southern littoral of the Persian Gulf, and continues to flourish among post-revolutionary diaspora communities in America, Asia, and Europe.