The BBC looks at two bitterly divided camps that have for years driven sporadic protests in Thailand - the red-shirts and the yellow-shirts.
The red-shirts began as supporters of deposed former Prime Minister Thaksin Shinawatra, who was ousted by a military coup in September 2006. This support has transferred to Thailand's ruling Pheu Thai party led by his sister, Yingluck Shinawatra.
The yellow-shirts represent those opposed to Mr Thaksin and they were the force behind the street protests that led to the 2006 coup.
The red-shirts are formally known as the United Front for Democracy Against Dictatorship (UDD). The focus of many red-shirts' campaigning zeal is former Prime Minister Thaksin Shinawatra.
Members are mainly rural workers from outside Bangkok. But the red-shirt ranks also include students, left-wing activists and some business people who see attempts by the urban and military elite to control Thai politics as a threat to democracy.
The source of the red-shirts' discontent goes back several years. They began as supporters of Mr Thaksin, the prime minister ousted by the military in a September 2006 coup.
By then Mr Thaksin - a telecommunications magnate - had governed Thailand for five years. He was very popular among the rural farmers and urban working class because he initiated policies that benefited them, such as funding for health-care and education.
When elections were held 18 months after the military coup, this rural support had not changed, even though Mr Thaksin was in overseas exile.
Voters from Thailand's north and north-east returned his allies to power, only to see the government fall after a series of opposition protests and court rulings. So the red-shirts began protesting.
Their first major protest began in March 2009 with a series of sit-ins outside government offices, but quickly escalated.
In April 2009 they forced the cancellation of a regional political summit after storming the venue in the seaside resort of Pattaya.
Violence then erupted in Bangkok. Clashes involving troops, protesters and Bangkok residents left at least two people dead and dozens hurt.
As troops massed, the red-shirts called off their protests. Leaders said they feared more loss of life.
But their anger had not gone away and, in March 2010, they called fresh protests in Bangkok aimed at toppling the government.
Tens of thousands of people occupied Bangkok's historic and commercial districts and at one point stormed parliament, forcing MPs to flee. Red-shirts also stormed a satellite transmission base, in a bid to restart a television station which had been shut down by the government.
The first bloodshed occurred on 10 April when at least four soldiers and 17 civilians were killed in clashes as the army tried to disperse the red-shirts from one of their two bases in Bangkok.
The violence shocked the city - but the red-shirts consolidated their forces in one camp, closing down the city's commercial heart for several more weeks.
On 19 May armed government troops moved into the red-shirt camp, smashing through barricades. By the end of the day, the camp had been cleared, several of the group's leaders arrested and dozens of people, including protesters and soldiers, killed.
A year on, many of their leaders have been released on bail.
The red-shirts are now allies of the ruling Pheu Thai Party. Yingluck Shinawatra, Mr Thaksin's sister, led the party to a landslide victory in July 2011 and became Thailand's first woman prime minister.
Like the reds, it was Thaksin Shinawatra that initially united the yellow-shirt camp.
A loose grouping of royalists, ultra-nationalists and the urban middle class also known as the People's Alliance for Democracy (PAD), the yellow-shirts utterly opposed Mr Thaksin.
They were behind the huge street protests that led up to the military coup of September 2006 and the ones two years later which led to Mr Thaksin's allies being forced from power.
Led by media mogul Sondhi Limthongkul, Chamlong Srimuang, who is a former general with close ties to the king's most senior adviser, the yellow-shirts accused Mr Shinawatra of corruption and abuse of power.
They also accused him of inadequate loyalty to the monarchy - and wear yellow because it is the king's colour.
Street protests in Bangkok in 2006 attracted tens of thousands of people, shutting the capital down. Amid political deadlock, the military ousted Mr Thaksin.
There was calm for several months. But rumblings began when Mr Thaksin's allies won the post-coup elections in December 2007 and formed a government.
In May 2008 the yellow-shirts restarted their protests, arguing that the government was merely a proxy for Mr Thaksin.
They staged sit-ins at government offices and there were sporadic outbreaks of violence.
In late November they staged a week-long sit-in at Bangkok's two airports, shutting down air traffic and crippling the tourism industry.
After weeks of pressure, a decision by the constitutional court decision finally achieved the yellow-shirts' goal. The pro-Thaksin governing party was banned for alleged electoral misdemeanours and a new Democrat Party government under Abhisit Vejjajiva took office.
The yellow-shirts called off their protests.
As the red-shirt occupation went on in 2010 - and in the months after it was ended - the yellow-shirt position towards the government of Mr Abhisit changed.
In January 2011 a group of about 2,000 began protests against his government, accusing him of failing to safeguard Thai sovereignty in a border dispute with Cambodia.
In June, the yellow-shirts blocked parliament to postpone debate on a reconciliation bill designed to ease a six-year political crisis, fearing that a proposed amnesty would allow Mr Thaksin's return.
They contend that the so-called reconcillation bill would grant amnesty to people guilty of political crimes between 2005-2010, when the country was in crisis.