The West African nation has been plagued by a series of military coups  [EPA]

Guinea-Bissau, one of the five poorest countries in the world, has a turbulent history.

A former Portuguese colony, the West African nation has witnessed three military coups since independence, and a brief civil war.

Analysts say a booming drugs trade has only worsened that instability in recent years.

UN drug experts say the tiny nation has become one of the key transit points for cocaine headed to Europe from South America.

Here are key dates in the country's history and current crisis:

July 1961: The African Party for the Independence of Guinea-Bissau and Cape Verde (PAIGC) launches a guerrilla war against Portuguese colonial rule.

January 20, 1973: Amilcar Cabral, the PAIGC leader, is assassinated by party dissidents. PAIGC unilaterally declares Guinea-Bissau independent.

September 10, 1974: The state of Guinea-Bissau is officially established and Cabral's brother Luis becomes president.

 
November 14, 1980: Joao Vieira, the prime minister, overthrows Cabral in a bloodless coup, and takes power at the head of a military "revolutionary council".

July-August, 1994: Country returns to civilian rule. Viera defeats Kumba Yala in first-ever multi-party presidential and legislative elections.

June-November, 1998: Army uprising against Viera's dismissal of the army chief sparks a civil war that displaces hundreds of thousands.

May 7, 1999: Soldiers remove Vieira from power in a dispute over implementation of the post-war transition, military government takes over.

November 28, 1999: Presidential election held. Yala wins most first round votes, followed by PAIGC leader Malam Bacai Sanha, who briefly led transition period. Yala wins runoff in January 2000 against Sanha.

September 14, 2003: Army chief of staff General Verissimo Correia Seabra declares himself interim president after the army seizes power and pledges to restore constitutional order following repeated delays to new elections. Yala formally resigns three days later.

July 28, 2005: Vieira is announced winner of July 24 runoff vote against Malam Bacai Sanha of the main PAIGC. Sanha's supporters say they reject the results, although PAIGC later accepts Vieira's return to power.

November 2, 2005: President Vieira names close ally, Aristides Gomes, as prime minister after sacking the administration of his political rival Carlos Gomes Junior on October 28.

March 29, 2007: Aristides Gomes resigns as prime minister after three main parties, PAIGC, Social Renewal Party (PRS) and the United Social Democratic Party (PUSD), sign up to a "stability pact" and carry a no-confidence vote against him.

February 29, 2008: PAIGC withdraws support for Prime Minister Martinho Ndafa Kabi, breaking year-old stability pact.

July 27, 2008: Opposition PAIGC announces it is pulling out of national unity government after its representatives are sacked from senior financial posts.

August 6, 2008: Rear-Admiral Jose Americo Bubo Na Tchuto, the head of the Navy, is suspended and put under house arrest.

August 8, 2008: Army says military officers tried to stage coup a week earlier. Na Tchuto and other officers being questioned.

November 23, 2008: President Vieira survives attacks by dissident soldiers armed with machineguns and rocket-propelled grenades. Interior ministry recruits a 400-strong presidential bodyguard.

January 4, 2009: One or more members of the militia shoot in the vicinity of the Armed Forces Chief of Staff Na Waie, although nobody is injured. Armed Forces Command says Na Wai was deliberately targeted and orders presidential bodyguard to be disbanded.

March 1, 2009: Na Waie killed in bombing of armed forces headquarters.

March 2, 2009: Vieira assassinated by soldiers at the presidential palace in presumed retaliation for the general's death. Na Waie was known to be critical of the president.

June 28, 2009: First round of presidential elections are held, but none of the candidates win majority of the vote.

July 26, 2009: People vote in a presidential runoff between two former heads of state.

Source: Agencies