Define 'Tatars' and define 'ancient Tatar lands' ))

Seriously though, there's a bunch of ethnic groups in Russia who could be considered Tatars, like Tatars proper, Bashkirs, Kumyks, Nogais, etc.

Paging /u/TenMinuteHistory and /u/wizzyhatz who have a good grasp of Russian and Soviet ethnic policies. But seeing that I've got an hour to kill, let's have a look at [the most recent population census in Russia (2010)] (http://www.gks.ru/free_doc/new_site/perepis2010/croc/perepis_itogi1612.htm) to see whether these 'Tatar lands' are indeed overrun by Russians.

Out of the total population of 141M in Russia over 5.3 million people identify as Tatars (i.e. Tatars proper / Volga Tatars / Kazan Tatars). That makes them the second largest ethnic identity in the country.

The Bashkirs are the fourth largest at 1.58 million.

The Chuvash are another major Turkic-speaking group although their language belongs to a different branch (it's Oghur while Tatar, Bashkir and there are Kipchaq languages) and they are traditionally Orthodox Christian rather than Sunni Muslim. But well, if we count them in, they are the fifth largest identity in Russia at 1.43 million[1].

Smaller groups include the Kumyks (0.5M), the Karachays (218K), the Balkars (113K), etc.

Now let's parse ethnic identities by some of the Tatar-heavier areas.

Tatarstan: Tatars proper are the majority and the language is co-official with Russian.

Out of the total population of 3.78M you've got 2M Tatars, 1.5M Russians. Also, 116K Chuvashes and 13.7K Bashkirs.

Largest spoken languages: Russian (3.68M), Tatar (1.97M), Chuvash (0.1M).

Bashkortostan: Total pop: 4M.

Largest identities: Russian (1.43M), Bashkir (1.17M), Tatar (1M), Chuvash (107K).

Spoken languages: Russian (3.91M), Tatar (1.06M), Bashkir (0.93M, co-official language).

Chuvash Republic Total pop: 1.25M.

Largest identities: Chuvash (815K), Russian (323K), Tatar (34K).

Spoken languages: Russian (1.183M), Chuvash (680K, co-official), Tatar (34K).

Ulyanovsk oblast Total pop: 1.2M.

Largest identities: Russian (0.9M), Tatar (0.15M), Chuvash (0.09M).

Spoken languages: Russian (1.2M), Tatar (0.08M), Chuvash (0.05M).

Orenburg oblast Total pop: 2M.

Largest identities: Russian (1.52M), Tatar (0.15M), Kazakh (0.12M). Also Bashkir (0.05).

Languages spoken: Russian (2M), Tatar (0.09M), Kazakh (0.05M).

Chelyabinsk oblast Total pop: 3.5M

Largest identities: Russian (2.83M), Tatar (0.18M), Bashkir (0.16M).

Spoken languages: Russian (3.37M), Bashkir (0.09M), Tatar (0.08M).

Karachay Cherkessia Total pop: 477K

Largest identities: Karachay (194K), Russian (150K). Other Tatar groups include Nogais (15K) and Tatars proper (2K).

Spoken languages: Russian (470K), Karachay-Balkar (186K, co-official) and others. Nogai is co-official.

Kabardino-Balkaria Total pop: 857K

Largest identities: Kabardian (490K, non-Turkic), Russian (193K), Balkar (108K).

Spoken languages: Russian (820K), Kabardian (438K, co-official), Karachay-Balkar (101K, co-official).

Dagestan Total pop: 2.9M. Over 30 indigenous languages spoken, 13 are co-official with Russian.

Largest identities: Avar (850K, non-Turkic), Dargin (490K, non-Turkic), Kumyk (aka Dagestan Tatars, 431K). Russians are only the 8th largest group at 102K. Nogais are the 10th largest at 40K.

A few points to bear in mind:

• Tatar elites have been co-opted and assimilated in Muscovy/Russia/the USSR since the 15th century. See [my comment here] (https://www.reddit.com/r/AskHistorians/comments/4mv9u2/when_did_the_russian_empire_begin_to_expand/d41p27z) on the curios case of Kasimov Tatars.

• Most Tatar khanates were conquered and incorporated in the 1500s, centuries before the modern concept of what it means to identify as a Tatar or Bashkir or whatever emerged.

• The data above is on a federal subject level which is, roughly, the Russian equivalent of a US state. In fact, most Tatar groups still live in contiguous areas that do not correspond to federal subjects. If we look at the same census data visualised by district (I think), you can see where they still are the majority. See [the Bashkirs] (https://upload.wikimedia.org/wikipedia/commons/3/35/Ареал_расселения_башкир_в_Волго-Уральском_регионе._По_данным_Всероссийской_переписи_населения_2010_года..png)], for example. Or [the Chuvashes] (https://upload.wikimedia.org/wikipedia/commons/5/5d/Ареал_расселения_чувашей_в_Волго-Уральском_регионе._По_данным_Всероссийской_переписи_населения_2010_года..png).

• Apart from the cities of Kazan and maybe Ufa, most folk who identify as Bashkir, Chuvash etc, would probably live in the villages. Most urban population is more likely to be of mixed heritage and to identify as 'Russian', the default identity, if you will. For a sample of a normal mix in a multi-cultural city let's look at the largest groups in Moscow. Out of the 10.8M who bothered to answer the question the three largest identities are Russian (9.93M), Ukrainian (154K) and Tatar (149K).

• Off the top of my head I can't think of a major massacre that you imply must have taken place.

• Stalin's displacement policies as proposed by /u/HeavyManCrush would only affect the Crimean Tatars who were forcibly exiled during WWII. But they were not in the majority in Crimea even before that and Crimea was only conquered in the late 1700s unlike the Eastern khanates and the Nogai Horde. Also, Crimea is very much of a special case as to whether it could be considered an 'ancient Tatar land'.

• Soviet-era policies must have had an influence but mostly wrt to industrialisation rather than some imagined displacement policies. More Russians, Ukrainians etc would be moving in to work at all those new factories and live in those growing cities, affecting the perceived identity balance. In this regard Tatars are a curious case as they quite a lot of them are urban folks (and they were/are quite heavy in the oil industry all over the USSR/Russia with many moving to work the new oil fields in Siberia, for instance). Here are the 2010 numbers (note that the country as a whole is largely urban): Tatars - 3.6M urban vs 1.7M rural. Bashkirs - 732K urban vs 852K rural. Chuvash - 704K urban vs 732K rural. Kumyks - 254K urban vs 249K rural. Karachays - 86K urban vs 132K rural. Balkars - 52K urban vs 61K rural.

tl;dr: They were not massacred and still live roughly where you expect them to. But Russians and other ethnic groups moved in, too. Also, intermarriage and assimilation.

[1] In case you're interested, the third largest identity is Ukrainian (1.93M). Chechens are the sixth largest group and are only insignificantly less numerous than the Chuvashes (1.431M vs 1.435M).