Thousands die and tens of thousands are displaced every year by a conflict which started in the mid-1960s as an uprising about inequality and poverty but has turned into a seemingly interminable war that encroaches on rural villages and isolated indigenous communities, creates urban slums and leaves even the privileged living in fear.

The main players are left-wing guerrillas funded by drug trafficking or kidnapping, right-wing militias initially formed to protect landowners from the guerrillas, an army bent on cracking down on rebels and their supporters, and cocaine cartels who run their own kingdoms using the cover of jungle and are beyond the reach of overstretched security forces.

A hefty portion of Colombian cocaine ends up on the streets of the United States, and the U.S. government gives heavy backing to Colombia's war on drugs, fuelling controversy among rights activists and environmentalists.

Colombian villagers often come under heavy pressure to turn to one armed group or another for protection, but are then vulnerable to reprisal attacks and massacres.

It's hard to pin down exactly how many people have fled rural violence or been forced off their lands by encroaching drug production, because many of the displaced are undocumented, living with relatives or melting into shanty-towns on the edge of Colombia's cities.

The government estimates more than 1.97 million Colombians have been displaced since 1994, but human rights groups say the figure is much higher - the Human Rights and Displacement Consultancy (CODHES) calculates about 3.9 million since 1985, as the Internal Displacement Monitoring Centre reports.

About 486,000 Colombians have fled to neighbouring countries - primarily Ecuador and Venezuela, but also Brazil, Costa Rica and Panama - according to January 2008 estimates from the U.N. refugee agency (UNHCR).

Human rights organisations say Afro-Colombians and indigenous peoples - among the poorest sectors of Colombian society - are disproportionately affected by displacement.

Armed groups and drug traffickers take cover in Colombia's vast jungles, endangering a number of small, isolated indigenous peoples whose traditional way of life revolves around rivers and the forest and rarely brings them into contact with outsiders.

Indigenous peoples make up just one percent of the population, but live in 27 of the country's 32 departments. UNHCR says there is a real threat of extinction for tribes such as the Wounaan who live in Choco near Colombia's northern border with Panama and the Nukaks who live in the southeastern department of Guaviarre.

Other peoples under threat are the Awa, Kofan, Siona, Paez, Coreguaje, Carijona, Guayabero, Muinane-Bora, Pasto, Embera and Witoto.

In this highly militarised countryside, civilians suffer a heavy toll from landmines, giving Colombia one of the world's highest landmine casualty rates.

In 2006, Colombia topped the table for landmine deaths and injuries with a total of 1,106, according to the Landmine Monitor, followed by Afghanistan with 488 and Pakistan with 796.

This isn't a straightforward two-sided war between government and revolutionaries, and it doesn't even divide neatly between left and right on the political spectrum, although politics is certainly an element of it.

Marxist rebels have been fighting to overthrow the Colombian government since the mid-1960s. While the guerrillas have changed considerably in many ways, the inequalities that originally fuelled revolt and attracted people to the cause haven't changed much.

The country's elite is drawn primarily from descendants of the Spanish, while people of mixed heritage - indigenous, African and European - tend to be less well off, and 18 percent of Colombia's population of 44 million live on less than $2 a day, according to the U.N. Development Report for 2007-2008.

Despite undeniable inequalities in land and wealth distribution, the guerrillas don't command much popular support, especially in urban Colombia, where the U.N. Population Division says more than 72 percent of the population lives.

Revolutionary Armed Forces of Colombia (FARC) is the larger guerrilla organisation, with around 10,000 to 11,000 fighters, according to analysts at International Crisis Group. It dominates a third of the country, with a strong presence in jungle regions in the south and east.

However, it's got significantly weaker since losing a series of top commanders, and hundreds have deserted from its ranks prompted by military pressure and government rewards.

FARC started as a group of Marxist revolutionaries, but became heavily involved in the drugs trade to fund its activities, and grew fat on cocaine money in the 1990s.

FARC has shown little interest in peace talks. It has repeatedly called for the government to remove troops from a vast rural area before it starts talks on exchanging jailed rebels for hostages.

President Alvaro Uribe believes the rebels would use a demilitarised zone to regroup and rearm as they did in the late 1990s when former President Andres Pastrana agreed to pull troops out of a jungle area the size of Switzerland. But he has offered a smaller haven under international observation in an area where there are no armed forces or armed groups.

Several kidnap victims were released in early 2008 after Venezuelan-brokered deals, the first time FARC had freed high-profile hostages.

Ingrid Betancourt, captured while campaigning to be president in 2002, was freed by the Colombian military in July 2008, along with a dozen others.

FARC still has scores of other hostages, some of whom have been held for more than a decade.

Peace overtures have been slightly more successful with the National Liberation Army (ELN), whose strongholds are primarily in northwestern Colombia near the Venezuelan border.

The ELN was formed by radical students and Catholic priests inspired by the Cuban revolution, and was heavily influenced by Liberation Theology, a radical form of Latin American Catholicism which flourished in the 1960s but was heavily suppressed throughout the continent.

The ELN rejects drug trafficking but is not above kidnapping to raise funds. It attacks oil pipelines and electrical pylons. It is much smaller than FARC, with about 2,200 to 2,500 rebels, according to International Crisis Group.

Observers say FARC and the ELN rarely work together, and compete for local support in some areas, but they don't often clash directly.

In the mid-1960s, and again in the 1980s, landowners set up vigilante groups to protect themselves and their property from the ELN and FARC. These evolved into brutal paramilitary organisations with their own hierarchical structures, and have also become heavily involved in the lucrative drugs trade.

The last members of the United Self-Defence Forces of Colombia (AUC) - the largest paramilitary organisation, with 30,000 members - handed in their weapons in 2006, under a deal with the government promising them freedom in civilian life or reduced jail sentences for crimes including murder in return for confessions and the return of illegal goods.

Once-semi-secret connections between the paramilitaries and the political establishment have been thrust into the limelight since former militia leaders started giving evidence about their high-profile friends.

The AUC, FARC and ELN are all designated terrorist organisations by the United States, and the Colombian army attracted U.S. support - military backing and training - during the Cold War for its anti-communist crusade.

The United Nations and many analysts say the demobilisation has not ended the AUC's influence or dismantled its criminal and cocaine-smuggling operations.

There are also several thousand other far-right paramilitaries who are not AUC members and have yet to hand in their weapons. Worse still, Belgian-based think tank International Crisis Group says the void left by demobilising groups who protected drug operations has created a demand for new illegal armed structures with names like "Black Eagles" and "New Generation", which are already recruiting ex-combatants.

The Organisation of American States said in a 2007 report that 22 new organisations had up to 3,000 members.

President Uribe came to power on a pledge to wipe out the insurgency, and initially showed little sign of compromise, launching the "Patriot Plan" in 2004 in a renewed crackdown on guerrillas and an attempt to break FARC's strength in southern Colombia.

Uribe promoted new legislation - the Justice and Peace Law - which came into force in July 2005, providing for the demobilisation of combatants, help for them to make the transition to civilian life, and compensation for victims of war crimes.

Under the new law, Justice and Peace Units are responsible for trying ex-militia members.

There's a separate National Commission for Reparation and Reconciliation. According to International Crisis Group, "Its priorities are discovering the truth regarding the death and disappearance of paramilitary victims, finding ways for reparation and paving the way for national reconciliation." The Catholic Church has independently compiled a confidential database of human rights violations.

However, rights activists say the law is weak and doesn't provide enough incentive for ex-combatants to confess, or give any guarantee that ex-combatants will really give up their weapons. They also say that women and children who worked with paramilitaries have been left out of peace deal benefits.

One of the reasons peace is so elusive is that life with the army or guerrillas or paramilitaries is a tempting career option for many poor people with scant options for making a living.

However flawed, most observers seem to agree the law is better than nothing.

Crisis Group says it will be hard for the government to comply with its commitment to compensate victims under the law. "To be blunt," a Crisis Group report says, "the law puts perpetrators first and victims second."

Colombia has been an important drug producer since the late 1970s, handling about 90 percent of the cocaine that ends up in the United States, according to U.S. government estimates.

Nearby Bolivia and Peru also grow coca - the plant that cocaine is made from - but there are some important differences. Firstly, coca leaves have some local cultural significance in these other countries, where they have been chewed for centuries as a stimulant that dulls hunger and decreases fatigue. This isn't the case in Colombia, where its production is almost entirely linked to the cocaine trade.

Secondly, Colombia not only grows the raw product, but processes it in clandestine hide-outs where environmentalists say toxic waste is dumped into the ground and pollutes water sources. Once it's on the way to becoming crack or cocaine, it's a far more potent drug, and the profit margin is far higher.

Colombia's drug traffickers have no scruples about kicking villagers off their land in order to turn it into new drug sites, and much of the trade is controlled by FARC and paramilitaries.

Since the armed groups get their income from drugs and kidnapping, they don't really need popular support, and they don't have much to gain from giving up their lucrative business.

The United States, which says Colombia is also a source of heroin, has weighed in heavily on the war on drugs, giving Colombia about $5.5 billion in aid since 2000. But critics say the U.S. assistance beefs up military operations which often have repressive effects on civilians. The Colombian government says aid just provides funds to escort its anti-narcotics operations.

A campaign to eradicate coca crops by aerial-spraying heavy-duty chemicals has had mixed results. The U.S. government says sprayed areas rarely come under cultivation the following year, but its own research shows that drug traffickers are constantly expanding into new zones, cutting down forests and displacing communities as they go.

The U.N. Office for Drugs and Crime said 99,000 hectares of Colombian land was being cultivated for coca in 2007. That's more than 10 percent of the country, equivalent to an area about the size of Cuba or South Korea.

Environmentalists are concerned about the environmental and health effects of spraying on non-drug crops and people who live in the areas, which include national parks.

Uribe is popular for cracking down on violence, which plagues Colombians from all walks of life. He won a second term in office in 2006 elections.

Violent crime has fallen considerably during Uribe's administration, but the figures still make sobering reading, with more than nine kidnappings every week.

"There is not a single person in Colombia that has not in one way or another been affected by the levels of violence in the country," Pierre Krahenbuhl, International Committee of the Red Cross director of operations, said in 2006.

The Vice President's Office says police recorded 486 kidnappings in 2007, compared to 687 in 2006. The 2006 total was an improvement on the 800 reported cases in 2005, and that, in turn, was a significant decrease from 2004, when there were 1,440 reported kidnappings.

A lot of kidnap victims don't make it home alive, even if their families pay a ransom. Many of the targets are fairly wealthy, since Colombia is a middle-income country with a substantial middle class and a sizeable elite living in relative luxury with armed guards in gated neighbourhoods.

But the poor are just as vulnerable to violent crime, in a country where the Vice President's Office says 17,198 people were murdered in 2007, down slightly from the 17,479 murders it claims for the previous year. The 2006 murder total was 17,281, a drop from 18,111 the previous year.

Despite the encouraging trend, Uribe has some critics among human rights organisations, who say his hardline approach infringes on human rights and sometimes tars trade unionists and community activists with the same brush as armed insurgents.

More than 4,000 trade union leaders have been assassinated since 1986, according to the U.S. State Department.

It's a risky country to be a journalist, too, with reporters frequently targeted for exposing corruption.

Rights campaigners also complain that the government's policies haven't stopped the need for people to flee danger in the countryside, or done anything to help hundreds of thousands of displaced people forced into near-destitution in urban slums.

Colombia has lived through periods of intense violence virtually since independence from Spain. The country's two main political parties - the Liberals and the Conservatives - were involved in bloody conflicts after their formation in the mid 19th century, even though their ideologies were almost indistinguishable.

Around 120,000 people died in "The War of a Thousand Days" between 1899 and 1903, and then another 300,000 people were killed in another period of civil conflict between 1948 and 1957.

After this, the two parties agreed to alternate power to end the battles and banned all other parties. The country has a democratic system now, but some analysts argue that Colombia has never known real democracy or rule of law, and that's one reason why it's so hard to achieve peace.