The North Caucasus region is the part of Russia that slopes up towards the main ridge of the Caucasus mountains, often considered the border between Europe and Asia.
It is home to dozens of nationalities and languages, many of which have troubled relationships with their neighbours or with central governments in Moscow or Tbilisi.
CHECHNYA
Status: Republic within Russian Federation
Population: 1.1m (figure is disputed)
Capital: Grozny
Languages: Chechen, Russian
Major religions: Islam
Chechnya declared independence from Russia in 1991.
Three years later the Kremlin sent in the troops to restore its authority, sparking the first Chechen war, which saw the capital Grozny reduced to ruins. It ended in humiliating defeat for the Russian forces in 1996.
In 1999, Russian troops rolled back in after Chechen militants crossed into neighbouring Dagestan in an unsuccessful attempt to start an armed uprising. Rebel commanders, who had governed Chechnya since elections in 1997, resumed a guerrilla war.
Major attacks blamed on Chechen separatists include: the deadly 2004 siege at a school in Beslan, North Ossetia, the mid-air destruction of two Russian civilian airliners, the bombing of a Moscow metro train as well as the seizing of a Moscow theatre in October 2002.
Chechen warlord Shamil Basayev is suspected of being the mastermind behind many of these operations.
Russian forces in Chechnya have been accused by human rights groups of committing widespread abuses against the general population. There are many reports of rape and summary execution, and of men disappearing, never to be seen again, as a result of Russian security operations.
The first Chechen rebel leader, Dzhokhar Dudayev, was killed by a missile in the mid-1990s. The next rebel leader, Aslan Maskhadov, was shot in March 2005, and his successor Abdul Khalim Saydulayev was killed in June 2006.
Moscow fears that if Chechnya broke away it could provoke demands for independence elsewhere in the region and become a centre of lawlessness and Islamic militancy.
INGUSHETIA
Status: Republic within Russian Federation
Population: 468,900
Capital: Magas
Languages: Ingush, Russian
Major religions: Islam
In 1936, under Soviet rule, Ingushetia was joined to Chechnya.
The Ingush and Chechen peoples have close historical, cultural and linguistic ties and both were deported to Central Asia in 1944 by Stalin who accused them of collaborating with the Nazis. Most of them returned in the 1950s.
At the time, Soviet authorities redrew the boundaries giving some Ingush land to North Ossetia - an act which sowed the seeds for a bitter conflict half a century later.
In 1992, Ingush forces moved in to the disputed Prigorodny district. Moscow sent troops to establish order and the Ingush population was expelled from the disputed areas.
Ingushetia lives in the shadow of the violence and lawlessness of its Chechen neighbour, and from time to time the violence spills over the border.
In June 2004, several dozen people, including an Ingush minister, were killed in attacks reported to have involved hundreds of armed fighters loyal to the Chechen warlord Shamil Basayev.
NORTH OSSETIA
Status: Republic within Russian Federation
Population: 709,900
Capital: Vladikavkaz
Languages: Ossetian, Russian
Major religions: Christianity
Historically, the North Ossetians, who speak an Iranian language, have had closer relations with Moscow than any other republic in the region.
North Ossetia is the most industrialised and urbanised republic in the North Caucasus.
In 1992, tens of thousands of ethnic Ingush were forced to flee North Ossetia after a bloody conflict between Ingushetia and North Ossetia. A peace agreement has yet to be reached.
Allegations that Ingush fighters were part of the armed group which took more than 1,000 hostages at a school in the North Ossetian town of Beslan in 2004 have led to renewed tensions between two communities.
North Ossetia has also had problems with large-scale criminal violence. A 1999 nail bomb attack on the central market in the capital, Vladikavkaz, killed 60 people.
DAGESTAN
Status: Republic within Russian Federation
Population: 2,584,200
Capital: Makhachkala
Languages: Dagestani group of languages, Russian
Major religions: Islam
Dagestan is the largest and most ethnically and linguistically diverse of all Russia's North Caucasian republics. It is also a conduit for oil exports from the Caspian Sea.
It is sometimes known as the Mountain of Languages, or Mountain of Nationalities - with some national groups occupying no more than one or two villages.
Dagestan kept out of the first Chechen war, though it was used by the Chechens as a supply corridor.
In 1999, home-grown Muslim radicals were joined by guerrillas from Chechnya in an attempt to establish an Islamic state that was quickly stamped out by the Russian army.
Since then, Dagestan has been the scene of a number of bloody attacks - including one at a Victory Day parade in 2002 - and hundreds of kidnappings.
KABARDINO-BALKARIA
Status: Republic within Russian Federation
Population: 900,500
Capital: Nalchik
Languages: Kabardian, Russian
Major religions: Islam, Christianity
Two ethnic territories form Kabardino-Balkaria: one predominantly of Kabardin (who speak a Caucasian language) and the other predominantly Balkar (who speak a Turkic language). There is also a significant Russian population.
In 1944, Stalin accused the Balkars of collaborating with Nazi Germany and deported the entire population, removing their name from the republic's title. They were only allowed to return in 1957.
Friction between the two communities is rarely far from the surface.
In 1992, the Balkars - who account for about 8% of the population - voted for secession. Their 1996 proclamation of a new republic received little support in Kabardino-Balkaria itself, but was generally backed in Chechnya.
In October 2005 Chechen rebel leader Shamil Basayev orchestrated a major attack on Nalchik, the capital of Kabardino-Balkaria, in which dozens of rebels and members of the security forces died.
SOUTH OSSETIA
Status: Region within Georgia
Population: 70,000 (approx)
Capital: Tskhinvali
Languages: Ossetian, Georgian, Russian
Major religions: Christianity
Although they live in the Southern Caucasus (south of the main ridge of the Caucasus mountains), South Ossetians are closely related to their northern neighbours.
South Ossetia was one of the first flashpoints of ethnic conflict in the disintegrating Soviet Union when, in 1990, calls for unification with North Ossetia led to conflict with Georgia's new nationalist government.
Up to 1,000 people died in two years of fighting. South Ossetia was relatively peaceful until mid-2004, when the conflict briefly flared up again.
South Ossetia's independence remains unrecognised but separatists hope for support from Moscow. Russia still has peacekeeping forces there and has close contacts with South Ossetian leaders.
ABKHAZIA
Status: Autonomous republic within Georgia (until 1992)
Population: 536,000 before 1992, 250,000 after 1993
Capital: Sukhumi
Languages: Russian, Abkhaz
Major religions: None
Though geographically in the South Caucasus, Abkhazia's strongest kinship links are with North Caucasians.
Abkhazia drove Georgian government troops out of its territory in 1993, a year after they launched an armed intervention to halt Abkhazian moves towards increased autonomy. More than 200,000 ethnic Georgian inhabitants of the region fled.
Two Chechen battalions under the commander Shamil Basayev supported the Abkhaz in this war, which enabled them to enter the Chechen war against Russia in 1994 as battle-hardened units.