By Kathryn Westcott BBC News Online

The Shia Muslim Arabs of the south as the majority group will expect, for the first time, to play a major part in a new administration, while the Kurds of the north may seize the chance to cement their autonomy. For the thousands of displaced minorities, the regime change could present an opportunity to simply return home.

This minority, which constitutes barely 20% of the population, has wielded power over the Shia Arab majority and the Kurdish minority since Iraq was created by the British in 1921.

Saddam Hussein's ruling Baath Party is dominated by Sunni Muslims

Their domination dates back to the time when Sunni Ottomans took control of the region in the 16th Century.

More recently, when the governing Baath Party came to power in 1968, it was controlled by Sunni Arab clans from provinces in north-western Iraq.

Among them was Saddam Hussein, whose power extended through his Sunni Arab family, extended family and his clan, the Tikritis from the small town of Tikrit on the Tigris north of Baghdad.

IRAQ'S PEOPLE Arabs comprise 75-80% of the population Kurds make up 15-20% Other ethnic minorities, such as Turkmen and Assyrian, 5% 95% are Muslim, 5% Christian and other minorities

Sunnis dominated the country's central region with its politics, the army and administration and many branches of the security services.

Another large Sunni clan that wielded power was the Dulaimi clan, which made up most of the regime's security and intelligence personnel.

They also led civil unrest and coup attempts against the president. Some 150 soldiers and officers were executed in 1995 after they revolted in response to the execution of a Dulaimi air base commander accused of planning to kill the president.

Sunnis tend to be secularist leaning.

Shia Arabs make up between 55% and 60% of the population. They are predominantly in south-east Iraq, around the city of Basra, but also make up a sizeable minority of the population of Baghdad.

Shia Muslims are the largest community in the country

They have historically been dominated and at times oppressed by the Sunni elite, who have excluded them from the highest ranks of power.

During Saddam Hussein's reign, Shia opposition groups were fiercely oppressed and a number of political leaders assassinated.

As a result, the opposition tended to look to neighbouring Iran for support, and in the late 1970s, thousands of Shia were expelled to Iran under the pretext of their "Persian connections".

HOLY CITIES Najaf, 190km south of Baghdad, was once the Shia power centre Karbala, 80km southwest of Baghdad, replaced Isfahan in Iran as the centre of Shia scholarship

The Iranian-backed Supreme Council for Islamic Revolution (Sciri) in Iraq is the strongest political group and claims to represent much of the Shia population. It has between 5,000 and 10,000 troops - known as the Badr Brigades - based mainly in Iran.

The group is led by Muhammad Baqir al-Hakim, whose followers have waged a low-level war of ambushes, sabotage, and assassinations against Saddam Hussein's regime for 20 years.

As the country's majority group, Shia are expecting a major say in the post-Saddam administration.

Shia form a sizeable minority in Baghdad

In 1991, after the first Gulf War, President Bush senior encouraged Iraqis to rise up against their leader. The opposition, including the Kurds of the north, believed this would mean the US would back a rebellion.

The Badr Brigades crossed the border into southern Iraq and Shia strongholds, including the holy city of Najaf on the Euphrates, rose in revolt. Lacking US support, it was brutally suppressed.

The Shia have been protected by no-fly zones in the south, patrolled by British and American fighter planes.

Before the Gulf War in 1991, Christians comprised almost one million of the Iraqi population.

Chaldeans are one of the largest Christian communities

Today, there are an estimated 650,000 Christians and all the churches report that number is still shrinking, as many continue to leave the country.

Many left to join relatives in the West after the first Gulf War and the imposition of economic sanctions against Iraq.

Assyrian (see separate entry) and Chaldean Catholics - who acknowledge the supremacy of the Catholic Pope - are the largest Christian communities. They can trace their ancestries to ancient Mesopotamia and the surrounding lands.

Other Iraqi Christians include Syrian Orthodox, Syrian Catholics and Greek Catholics and the Armenian Apostolic Church.

DWINDLING MINORITY Christians used to number one million Today there are an estimated 650,000 The constitution allows freedom of religion

Many Christians can be found in the northern cities of Kirkuk, Irbil and Mosul, but there are also a significant number in Baghdad.

Christians rose to the top ranks in Iraq under Saddam Hussein, with Deputy Prime Minister Tariq Aziz prominent among them. Commentators say anti-Christian violence was largely suppressed by the Baath regime.

Iraq's Christian communities have lived in harmony with their neighbours for decades. In Mosul, for example, there are an estimated 50,000 Christians.

The city - Iraq's third-largest and a centre of the oil industry - is also home to Muslim Kurds, Turkmen and Arab Muslims.

But some communities were subjected to the government's systematic "relocation programmes". For the Christians, this was particularly marked in the oil-rich areas, where the government tried to create Arab majorities near oil fields to secure control of economic assets.

Some Christians feared that the US-led war conflict in the country might generate anger against them. They recalled the first Gulf War, when "New Crusaders" was how many Muslims sympathetic to Saddam Hussein described the American and allied forces.

Kurds are members of an ethnic group that mainly inhabit south-eastern Turkey, north-western Iran, northern Iraq and parts of Syria.

Many Iraqi Kurds have fled the country for Europe

They are descendants of Indo-European tribes and appear in the history of the early empire of Mesopotamia. They trace their distinct history as mountain people to the 7th Century BC.

Kurdish nationalism manifested itself in the late 19th Century, but the aspirations of Kurdish nationalists have remained unfulfilled. Together, they make up the world's largest ethnic group without a state.

They are predominantly Sunni Muslim, a religion that was embraced by the Kurds around the 7th Century AD.

Iraqi Kurds, who make up 15% to 20% of the country's population, have been fighting for self-rule from Baghdad since 1961.

STATELESS PEOPLE Kurds are the largest ethnic group without a state Others live in Turkey, Syria and Iran Some 3.5 million live in the no-fly zone

In 1970, an agreement between Kurdish leaders and the Iraqi Government paved the way for the Kurdistan Autonomous Region (KAR) to be set up in northern Iraq four years later.

After the 1991 Gulf War, Baghdad lost its control of the KAR and, with the protection of American and British planes keeping Saddam Hussein's forces at bay, the Kurds formed a de facto state in the mountains.

Kurds have been victims of military campaigns by the former central government.

During the 1980-88 Iran-Iraq war, Kurdish guerrillas stepped up their opposition against the regime, with help from Iran. The Iraqi president deployed troops in the north in response.

In 1988, he unleashed a seven-month campaign against strongholds belonging to one of the main Kurdish parties, involving use of chemical weapons affecting thousands of villages.

In March of that year, at least 5,000 Kurds perished in one hour when forces dropped chemical bombs on the eastern town of Halabja.

And, in 1991, after the first Gulf War, Kurdish nationalists persuaded the local army auxiliary force comprising Kurds to change sides and take part in a rebellion. But the insurrection was crushed, causing an exodus of about 1.5 million Kurds into Iraq and Turkey.

The Kurds make up the bulk of the estimated nearly one million Iraqis who were displaced during Saddam Hussein's rule.

These systematic displacement programmes were conducted by the Baath Party in an attempt to control the oil-rich areas in the north of Iraq.

Policies included forcible expulsion or stripping families of identities, property documents and food ration cards. Many fled the country or ended up in squalid camps for displaced people within the KAR.

The Kurdish enclave is controlled by two factions - the PUK in the north-east headed by Jalal Talabani, and the KDP which dominates the north-west and is headed by Massoud Barzani.

For the past 10 years the two have been bloody rivals, but recently signed a unity pact.

They constituted the greatest armed challenge to the old Iraqi regime - between them, the two groups could muster about 60,000 fighters.

The Kurds favour a post-Saddam constitution that envisages two federal regions, one in the predominantly Kurdish north and one in the Arab south.

But this would likely bring opposition from one of Iraq's powerful neighbours, Turkey, which, with its own Kurdish population of 12 million, is very sensitive about anything that could be construed as a Kurdish move towards independence.

The Marsh Arabs are mainly Shia Muslims who once inhabited the marshes around the southern reaches of the Tigris and Euphrates rivers.

Many of the Marsh Arabs have been displaced

They are believed to have lived in the ancient wetlands along the border with Iran for 5,000 years.

Marsh Arabs lived in houses made of lattice-worked reeds and survived by rearing buffalo.

But most of the original Marsh Arabs - who numbered around 250,000 a decade ago - have become displaced and much of the marshes drained.

Accessible only by boat until the advent of the helicopter, the marshlands were a traditional centre for banditry and rebellion.

During the Iran-Iraq war in the 1980s, they were an infiltration route for Iraqi opposition militias based in Iran.

SIMPLE LIFE Marsh Arabs lived in cathedral-shaped reed houses They raised buffalo and fished, when not taking part in Mesopotamian battles A unique culture was obliterated by drainage schemes

And in the days after the first Gulf War, many Marsh Arabs, along with hundreds of thousands of Shia in the south, rose up against Baghdad.

The rebellion was crushed and many marshland villages were bombed by Saddam Hussein's troops.

Shortly after, the Iraqi Government set about obliterating swathes of the marshes, which were systematically drained.

The former Iraqi regime said the draining of the wetlands was part of a massive irrigation scheme to improve the lives of the local population, but the UN environment programme concluded the intention was to simply drain the marshland dry.

At least 100,000 Marsh Arabs were displaced within Iraq and about an additional 40,000 fled to Iran.

The predominantly Muslim Turkmen are an ethnic group with close cultural and linguistic ties to Anatolia in Turkey.

They number about 2% of the population.

Turkmen began to settle in Mesopotamia in the 11th Century and number of communities were founded in Iraq in the 12th Century.

ANCIENT PEOPLE Settled in Mesopotamia in 11th Century Many have been displaced They are historically and culturally tied to Kirkuk

They live mainly in northern Iraq, particularly in the area around Mosul and Kirkuk - which it sees as its historical and cultural base - south of the Kurdish Autonomous Region.

The Baghdad Government had long tried to change the demography of the areas where Iraq's vast oil wealth lies by forcing Kurds and Turkmen out to be replaced by Arabs from southern Iraq.

Turkmen leaders say thousands of their community were forced into destitution in northern Iraq, while up to 20,000 made their way illegally to Europe throughout the 1990s.

Now that Saddam Hussein's regime is finished, Kirkuk could become the centre of a struggle between the Turkmen and the Kurds, both of whom have people who will want to return to their homes.

The Turkmen community's two main parties are divided in their support. One works in co-operation with the Kurdish authorities, the other is backed by Turkey and opposes a Kurdish state in northern Iraq - especially one that would adopt Kirkuk as its capital.

Assyrians are descendants of the ancient empires of Assyria and Babylonia. These empires ruled over what was known as Mesopotamia, roughly the same area as modern Iraq.

After the collapse of their empire during the 6th and 7th Centuries BC, the Assyrians scattered across the Middle East region.

Assyrian political parties campaign for more national rights

They embraced Christianity in the 1st Century and are today followers of the ancient church of the East, the Syrian Orthodox Church of Antioch, the Chaldean Catholic Church and various Protestant denominations.

Like the Armenians, they were victims of Ottoman massacres and in 1915 were driven by the Turks out of the mountainous region where they were living as a semi-independent people.

A year after Iraq became independent in 1932, the Iraqi military set upon the Assyrians resulting in large-scale massacres in retaliation for their collaboration with the British, the former colonial power.

Assyrians weren targeted as part of the Baath regime's internal deportation programmes to maintain a grip on the nation, particularly the oil-rich areas.

Hundreds of Assyrian villages were destroyed by Iraqi forces in northern Iraq, churches and monasteries were torn down and Assyrians denied the right to practise their religion and preserve their culture and language.

Recently, however, there appeared to have been some kind of reconciliation with the government. Some places of worship were rebuilt and the Assyrian culture appeared to have been tolerated.

There are five seats reserved for northern Christians in the Kurdistan National Assembly in the Kurdistan Autonomous Region. The most important party representing this group is the Assyrian Democratic Movement (ADM).

It campaigns for the recognition of Assyrian national rights and encompasses Chaldean, Assyrian and Syriac identities - which the party says are different names for one common identity.