(CNN)Here's some background information about Yemen, a country located on the southwestern tip of the Arabian Peninsula, sharing a border with Saudi Arabia and Oman.
(from the CIA World Fact Book)
Area: 527,968 square kilometers (slightly larger than twice the size of Wyoming)
Population: 26,052,966 (July 2014 est.)
Median age: 18.6 years
Ethnic Groups: Predominantly Arab, also Afro-Arab, South Asian, European
GDP: $106 billion (2014 est.)
GDP per capita: $3,900 (2014 est.)
Unemployment: 27% (2014 est.)
Yemen is one of the poorest countries in the Arab world, due to declining oil resources.
Qat, an addictive narcotic grown in Yemen, uses more than a third of the country's water supply. The United Nations predicts Sanaa, the capital, will run out of water by 2017, the same year a 2008 IMF/World Bank study predicts the country's oil to run out.
Yemen's economy depends on foreign aid and money sent home by Yemenis who are employed in other parts of the Arabian Peninsula.
Most Yemenis are farmers, herders or craftsmen.
Yemen is part of the Arab League.
The Houthis are a Shiite milita group, originating in northwest Yemen. They are followers of the Zaidi sect of Islam.
May 22, 1990 - The Republic of Yemen is created from unification of North Yemen, the Yemen Arab Republic (YAR), and South Yemen, the People's Democratic Republic of Yemen (PDRY).
April 1993 - Elections are held after postponement due to political turmoil.
May 1994 - A civil war between northerners and southerners begins due to disagreements between supporters of Yemen's president, Ali Abdullah Saleh, from North Yemen, and its vice president, Ali Salim al-Baid, from South Yemen. An estimated 5,000 people are killed. Troops loyal to Saleh win the war in July.
1998 - Worsening economic conditions contribute to increased militant Islamist activity in the late 1990s. In 1998, 12 tourists are kidnapped, four of whom are murdered. Troubles with al Qaeda and similar groups increase after this.
September 1999 - Saleh wins Yemen's first direct election.
2000 - Saudi Arabia and Yemen agree to a delineation of their border.
October 12, 2000 - The USS Cole, at anchor in Aden, is bombed by al Qaeda, killing 17 U.S. sailors.
October 2002 - Al Qaeda is blamed for an attack on the Limburg, a French-flagged oil tanker off the Yemeni coast.
August 2004 - A Zaydi rebellion erupts in northern Yemen.
February 2006 - Twenty three inmates escape from a prison in Sanaa. Thirteen are convicted al Qaeda members, including Jamal al-Badawi, who plotted the attack on the USS Cole.
September 23, 2006 - President Saleh wins re-election to a seven-year term with 77% of the vote.
September 17, 2008 - A suicide bombing at the U.S. embassy in Sanaa kills 16, including six terrorists and one American. It is the fourth time since 2003 that the embassy has been attacked.
December 28, 2009 - A Yemeni-based arm of al Qaeda, al Qaeda in the Arabian Peninsula (AQAP), claims responsibility for a failed bombing on a Northwest Airlines flight from Amsterdam to Detroit on Christmas.
January 2, 2010 - U.S. President Barack Obama announces a new counter-terrorism partnership with Yemen, involving intelligence sharing, military training and joint attacks.
January 3-5, 2010 - The United States and the United Kingdom temporarily close their embassies in Sanaa due to terror concerns.
February 11, 2011 - Protests begin in Yemen, inspired by the revolution in Egypt that ousted Hosni Mubarak. The demonstrations continue for months, while crackdowns on protesters lead to civilian deaths.
June 3, 2011 - Opposition forces launch missiles at the presidential palace, injuring President Ali Abdullah Saleh and killing several others.
June 6, 2011 - It is revealed that President Saleh is being treated for burns over 40% of his body and a collapsed lung.
September 2, 2011 - Approximately two million people demonstrate across Yemen, demanding that the military remove President Saleh from power.
September 30, 2011 - Anwar al-Awlaki, spokesman for al Qaeda in the Arabian Peninsula, is killed by a CIA drone strike eight kilometers from the town of Khashef in the Province of Jawf.
November 23, 2011 - President Saleh signs an agreement in Saudi Arabia transferring his executive powers to Yemen's vice president, Abdu Rabu Mansour Hadi, effectively ending his rule. He is allowed to retain the title of president for 90 days.
January 21, 2012 - Yemen's parliament approves a controversial law that ensures Saleh complete immunity from prosecution. In return, Saleh will step down from power next month.
February 21, 2012 - Yemen holds presidential elections to replace President Ali Abdullah Saleh. There is only one candidate on the ballot, Vice President Abdu Rabu Mansour Hadi, the acting president since November 2011. Hadi receives 99.8% of the 6.6 million votes cast.
February 25, 2012 - Abdu Rabu Mansour Hadi is sworn in as president of Yemen.
February 27, 2012 - The official inauguration of Hadi takes place.
May 21, 2012 - A suicide bomber attack in Yemen kills over 100 Yemeni troops and wounds more than 200.
May 23, 2012 - Donor countries led by Saudi Arabia and the United Kingdom calling themselves the "Friends of Yemen" pledge more than $4 billion in aid.
January 24, 2013 - The Yemeni government confirms that Saeed al-Shahri, second in command of al Qaeda in the Arabian Peninsula (AQAP), has died after being wounded on November 28, 2012.
December 5, 2013 - Militants stage a deadly attack on Yemen's Defense Ministry in Sanaa, ramming the building with an explosives-laden vehicle, followed by gunmen battling security forces inside. The attack targets a hospital at the Defense Ministry complex, according to the state-run Saba news agency. At least 52 people are killed in the attack, including four foreign doctors.
December 15, 2013 - Yemen's parliament calls for an end to drone strikes on its territory three days after a U.S. missile attack mistakenly strikes a wedding convoy, killing more than a dozen people.
February 10, 2014 - President Abdu Rabu Mansour Hadi approves making Yemen a federal state consisting of six regions: two in the south, and four in the more populated north.
April 22, 2014 - At least 65 suspected al Qaeda in the Arabian Peninsula (AQAP) militants were killed in a combination of recent firefights and U.S. assisted drone strikes in a multi-day operation which involved ground combat and drone strikes. Yemeni officials say the United States assisted in the ground operation but did not take part in combat. The United States did not comment, however CIA drones are suspected to have targeted the al Qaeda fighters, weapons locations and a training camp.
September 21, 2014 - President Hadi, a powerful rebel group and representatives of major political parties sign an "immediate ceasefire, ending all forms of violence," according to a written statement. The U.N.-brokered deal ends a month of tense protests by Houthis, anti-government protestors, that essentially halted life in Sanaa, the capital, and resulted in hundreds of people being killed or injured. Also, Prime Minister Mohammed Salem Basindwa submits his resignation.
January 17, 2015 - Houthi rebels kidnap presidential Chief of Staff Ahmed bin Mubarak in the capital, Sanaa in a push for more political power. He is freed 10 days later.
January 20, 2015 - Houthi rebels take over the presidential palace.
January 22, 2015 - President Abdu Rabu Mansour Hadi resigns shortly after his prime minister, Prime Minister Khaled Bahah, and the Cabinet step down. Houthis now control the capital, Sanaa.
February 11, 2015 - The United States, the United Kingdom and France suspend embassy operations in Yemen, citing a deteriorating security situation in Sanaa as well as terrorist activities and civil unrest.
March 20, 2015 - Terrorists bomb two mosques in Sanaa, killing 137 and wounding 357. ISIS claims responsibility for the attack.
March 21, 2015 - The United States evacuates the last of its special operations forces, according to the State Department.
March 22, 2015 - Houthi rebels seize the international airport in Taiz.
March 26, 2015 - Warplanes from Saudi Arabia, UAE, Kuwait, Bahrain, Qatar and other allies strike rebels in Yemen. Saudi Arabia also threatens to send in 150,000 ground troops. All of these countries are predominantly Sunni Muslim, whereas the Houthi rebels are Shite Muslim, and Yemen considers the Houthis proxies for the government of Iran.