Colombia has suffered decades of civil conflict and has long been the world's biggest producer of cocaine.
President Alvaro Uribe, who came to power in 2002 and was re-elected in 2006, has pursued a hardline stance against left-wing guerrillas while making tentative peace overtures.
In mid-2008, a series of setbacks suffered by the country's biggest rebel group, the Revolutionary Armed Forces of Colombia (Farc) suggested Mr Uribe's stance was having an effect.
But the kidnap and killing of Luis Francisco Cuellar governor of Caqueta province, by suspected Farc rebels, seem to confirm reports that the group has rallied under new leadership.
Under a separate peace deal, some 31,000 right-wing paramilitaries have disarmed but moves to complete the demobilisation process remain controversial and fraught with difficulties.
Nevertheless, Colombia, the centre of the world cocaine trade, remains beset by violence and poverty.
Why is Colombia so violent?
Colombia , in common with many Latin American nations, evolved as a highly segregated society, split between the traditionally rich families of Spanish descent and the vast majority of poor Colombians, many of whom are of mixed race.
This group provided a natural constituency for left-wing insurgents - who nowadays fall into two groups, the Farc and the ELN. (National Liberation Army)
At the other end of the political spectrum are right-wing paramilitaries, with roots in vigilante groups set up decades ago by landowners for protection against rebels. The main group was the AUC - the United Self-Defence Forces of Colombia.
Elements of all the armed groups have been involved in drug-trafficking.
In a country where the presence of the state has always been weak, the result has been a grinding war on multiple fronts, with the civilian population caught in the crossfire and often deliberately targeted for "collaborating".
Human rights advocates blame paramilitaries for massacres, "disappearances", and cases of torture and forced displacement. Rebel groups are behind assassinations, kidnapping and extortion.
It is difficult to find reliable statistics on the toll from the violence in Colombia. What is clear is that the scale of the suffering has been huge.
Especially at risk are those with high-profile roles in the community - including social leaders, political activists, human rights campaigners and trade unionists. Many indigenous communities have also suffered attacks.
Violent crime and kidnappings have, however, decreased in recent years. In May 2008, the government announced that kidnaps were at a 20-year low. Figures showed that from a high in 2000, when more than 3,500 people were seized, in 2007 just under 400 people were kidnapped. Of these, some 179 were freed.
But the fate of those taken hostage by rebels or seized by common criminals continues to resonate in Colombian society.
The UN says that many displaced people often end up living in shanty towns around the cities, where they have little access to health or educational services.
What are the prospects for peace?
Although there have been many attempts at negotiations over the course of the conflict, these have always faltered and the prospect of a negotiated solution still seems very distant.
President Uribe has pursued a tough security policy, a move that has won appreciation from many Colombians worn out by conflict. The Farc rebels have suffered a series of blows.
The audacious rescue by the Colombian military of the country's highest-profile hostage, Ingrid Betancourt, and 14 others in 2008 deprived the rebels of one of their biggest bargaining chips for obtaining the release of jailed rebels.
However, during 2009 the Farc and the ELN were able to show that they could launch attacks and were not a spent force.
What about paramilitary fighters?
Since 2003, some 31,000 paramilitaries have handed in their weapons under a peace deal.
A controversial justice and peace law passed in 2005 meant that paramilitary fighters were eligible for reduced jail terms - of no more than eight years - if they give details of their involvement in torture, killings and other crimes.
Critics argued that paramilitaries guilty of serious human rights violations could end up serving only token jail terms.
The government points to figures which it says show a decreasing level of violence as evidence that its strategy is working. It rejects accusations that it has been soft on the paramilitaries, and says the door is open to rebels wishing to engage in peace talks.
The extent of the paramilitaries' influence over and involvement in local, regional and national politics came to the fore in 2007.
In a scandal dubbed the "parapolitics", a dozen members of congress were jailed and dozens more politicians investigated for links to the AUC.
Why is the US involved in Colombia?
Up to 90% of all cocaine on American streets comes from Colombia, so the US administration is keen to tackle the supply at source.
Since 2000, Washington has spent some $6bn (£3.8bn) on Plan Colombia, under which Colombian forces receive training, equipment and intelligence to root out drug-traffickers and eliminate coca crops.
Initially, the US Congress stipulated that this money should only be used against drug lords and not for any other campaigns, such as the government's fight with left-wing rebels. However, since 2002 the Bush administration indicated that some aid was being spent on counter-terrorism.
Human rights groups say the line between the war on drugs and the war on rebels is increasingly blurred.
They say Colombia's rebels have been disproportionately targeted in Plan Colombia, though it is the paramilitaries who have been most involved in drug-trafficking.
The US and Colombia signed a controversial deal in October 2009 to allow the US military use of several Colombian airbases.
The two countries said this was to counter drug-trafficking and terrorism.
Some of Colombia's neighbours expressed concern at what they saw as an increased US military presence in South America.