Remember that in 1360 the Turks began to expand their holdings. By 1453 they had captured Constantinople. In 1648 the Turks had all of North Africa, the Levant, Mesopotamia, Asia Minor, Greece, all the Balkans, part of Austria, Hungary, Romania, Poland, Ukraine and the Crimea.
I beg to differ. The Ottoman Empire never held parts of 'Austria', although there were regions which came to Austria later on in history, but never did any of the Austrian mainlands belong to the Ottoman Empire. The sieges of Vienna in 1529 and 1683 both ended in the defeat of the Ottoman army.
Only the Southern part of Ukraine belonged to the Ottoman Empire, and this happened to be a Tatar Khanate with a widely Sunni Muslim population. The Khanate of Crimean Tatars was founded in 1430. It became Ottoman in 1475 already, and Russian in 1774.
The North of Ukraine never belonged to the Ottoman Empire. Poland also never belonged to the Ottoman Empire, neither in whole nor in part.
Although the Ottoman Empire began to fall rapidly at the end of the 19th century/beginning of 20th century, some of its conquests changed ownership (e.g. in the Balkans and North Afrika) before, and this process started much earlier. Following the defeat of the Turkish army at Vienna in 1683, the Pope initiated a so-called Holy League in 1684 (Austria, Republic of Venice, Poland-Lithuania) to launch counter-attacks, as the military crisis of the Ottoman Empire had become apparent, and battles in 1684 and the following years resulted in further territorial losses of the Ottoman Empire. The peace treaty of 1699 e.g. brought about the loss of Central Hungary to Austria, part of the Ottoman regions in Southern Ukraine came to Poland-Lithuania, Dalamatia to Venice. Already in 1695, Russia had gained an access to the Black Sea.
The Slavic regions were largely pagan.
The process of christianization of the Slavic regions started shortly after 800, and was completed by mid-9th century. Most of the countries became orthodox, while a minority (e.g. the Croatians, and Poland) were converted to Catholicism.
As far as Ukraine is concerned, it was a xtian country since July 28, 988, when Grand Prince Vladimir declared christianity the state religion on the day of his baptism. Vladimir belonged to the dynasty of Kiev Rus which actually was a predecessor of Russia. Ukraine made July 28 a national holiday at the 1000th anniversary in 2008.
To give two more examples:
Hungary's first xtian ruler was King Istvan I (Stephen) who lived from 969-1038. Systematic christianization in Hungary began in 973.
Bulgaria was a xtian country by 864 when King Boris I declared christianity the state religion. The Bulgarian realm was founded in 679, and at that time, there was a Thrakian population living in the country which had been Romanized, and this group of the country's population was xtian before 679.
There are areas of Europe and Asia which never became christian even to this day.
The areas we're discussing here would be European (the non-xtian regions in Asia being quite obvious) – so which areas are this? Apart from those with a traditional Muslim majority or minority, that is, like e.g. Albania, Bosnia, Bulgaria?
Christianization of Eastern Europe, as I said above, was completed by mid-9th century, and even earlier in Western Europe. This left only very few exceptions, like those peoples belonging to the Finno-Ugric language group living in the North of Russia. Their christianization even started before their conquest by Russia, as early as 16th century, (cf this map:
http://www.samojeden-kennel.ch/images/samvolk-sprachkarte.jpg ), although traditional religions were mixed with xtian religion.
Essentially the centuries of Turkish rule created large areas of neutrality with pagan beliefs kept intact and not christianised.
Unfortunately, this is pretty far from facts. The Ottoman Empire was a Muslim state, and in accordance with Islam, they tolerated those religions called the 'family of the book' (ahl al-kitab), i.e. Xtian and Jewish denominations. Pagan beliefs were not seen as equal to the book religions, and any pagan areas within the Ottoman Empire would have experienced pressure to convert to Islam. There is simply no chance that 'large areas' with pagan beliefs could have survived Ottoman rule.
Book religions, on the other hand, enjoyed religious freedom and were organized in so-called millets, sort of autonomous corporate bodies, which also kept their own jurisdiction to observe in law cases among themselves. In case of a member of such a millet being treated by Ottoman courts, the courts had to observe differences in jurisdiction.
However, the regions had been christianized before the Ottoman conquest, and largely remained xtian under Ottoman rule. The Muslim minority in Bulgaria e.g. was caused by Turkish settlers sent to Bulgaria by the Sublime Porte, but there was also a Muslim minority who lived there before, called the Volga-Bulgarians.
