Question: The Battle of Aden International Airport broke out when Army units loyal to former president Ali Abdullah Saleh attacked an airport in which country?

Context paragraphs:
Battle of Dhale: The Battle of Dhale was a key fight for control of Dhale, Yemen, between the Houthis and Yemen Army units loyal to Ali Abdullah Saleh on one side, and militiamen and Yemen Army units loyal to Abd Rabbuh Mansur Hadi on the other side.

Shabwah campaign (March–August 2015): The Shabwah campaign (March–August 2015) was a campaign for control of the Shabwah Governorate of Yemen, between the Houthis and Yemen Army units loyal to Ali Abdullah Saleh on one side, and militiamen and Yemen Army units loyal to Abdrabbuh Mansur Hadi on the other side.  The offensive have also launched during an previously started AQAP offensive.

Battle of Aden Airport: The Battle of Aden International Airport broke out in the early morning hours of 19 March 2015, when Yemen Army units loyal to former president Ali Abdullah Saleh attacked the airport in Aden, Yemen.  The airport was defended by soldiers and guards supporting Abdrabbuh Mansur Hadi, Yemen's internationally recognised president.

Yemeni Crisis (2011–present): The Yemeni Crisis began with the 2011–12 revolution against President Ali Abdullah Saleh, who had led Yemen for more than two decades.  After Saleh left office in early 2012 as part of a mediated agreement between the Yemeni government and opposition groups, the government led by Saleh's former vice president, Abdrabbuh Mansur Hadi, struggled to unite the fractious political landscape of the country and fend off threats both from Al-Qaeda in the Arabian Peninsula and Houthi militants that had been waging a protracted insurgency in the north for years.  In 2014, Houthi fighters swept into the capital of Sana'a and forced Hadi to negotiate a "unity government" with other political factions.  The rebels continued to apply pressure on the weakened government until, after his presidential palace and private residence came under attack from the militant group, Hadi resigned along with his ministers in January 2015.  The following month, the Houthis declared themselves in control of the government, dissolving Parliament and installing an interim Revolutionary Committee led by Mohammed Ali al-Houthi, a cousin of Houthi leader Abdul-Malik al-Houthi.  However, Hadi escaped to Aden, where he declared that he remains Yemen's legitimate president, proclaimed the country's temporary capital, and called on loyal government officials and members of the military to rally to him.  On 27 March 2015, BBC reported that Hadi had "fled rebel forces in the city of Aden" and subsequently "arrived in Saudi Arabia's capital Riyadh" as "Saudi authorities began air strikes in Yemen".

Ahmed Saleh: Ahmed Ali Abdullah Saleh Al-Sanhani Al-Humairi (Arabic: أحمد علي عبد الله صالح السنحاني الحميري‎ ‎ ; born July 25, 1972) is the eldest son of former Yemeni president Ali Abdullah Saleh, and was a commander of approx. 80,000 troops of the Republican Guard unit of the Yemen Army.  On April 14, 2015, the United States Department of the Treasury's Office of Foreign Assets Control added Saleh to the list of Specially Designated Nationals, barring US citizens and businesses from interacting with Saleh or his assets.

Ali Abdullah Saleh: Ali Abdullah Saleh (Arabic: علي عبد الله صالح‎ ‎ , "ʿAlī ʿAbdullāh Ṣāliḥ"; born 21 March 1942) is a Yemeni politician who rose to power following the assassination of President al-Ghashmi.  He was elected President of North Yemen (the Yemen Arab Republic) on 17 July 1978 at the age of 36.  Following the merger of North Yemen with South Yemen on 22 May 1990, President Saleh was sworn in as the new President.  Long considered a moderate President, he oversaw his country's development of deeper ties with Western powers, especially the United-States, in its fight against terrorism.  In 2011, in wake of the "Arab Spring" that spread across Yemen, Saleh's time in office became more and more untenable, until eventually he was ousted as President of Yemen in 2012.  He was succeeded in office by Abd Rabbuh Mansur Hadi.

Yemeni Civil War (2015–present): The Yemeni Civil War is an ongoing conflict that began in 2015 between two factions claiming to constitute the Yemeni government, along with their supporters and allies.  Houthi forces controlling the capital Sana'a and allied with forces loyal to the former president Ali Abdullah Saleh have clashed with forces loyal to the government of Abdrabbuh Mansur Hadi, based in Aden.  Al-Qaeda in the Arabian Peninsula (AQAP) and the Islamic State of Iraq and the Levant have also carried out attacks, with AQAP controlling swathes of territory in the hinterlands, and along stretches of the coast.

Abyan campaign (March–August 2015): The Abyan campaign (March–August 2015) was a campaign for control of the Abyan Governorate of Yemen, between the Houthis and Yemen Army units loyal to Ali Abdullah Saleh on one side, and militiamen and Yemen Army units loyal to Abd Rabbuh Mansur Hadi on the other side, supported by jihadists of al-Qaeda in the Arabian Peninsula.  The Pro-Hadi Forces recaptured the Abyan Governorate on 11 August, after launching an offensive on pro-Houthi forces in early August.

Lahij insurgency: The Lahij insurgency was a guerrilla war waged by tribesmen loyal to Abdrabbuh Mansur Hadi against the Houthis and Yemen Army units loyal to Ali Abdullah Saleh, who controlled most of the Lahij Governorate of Yemen.

Battle of Aden: The Battle of Aden was a battle for the control of Aden, Yemen, between the Houthis and Yemen Army units and militias loyal to Ali Abdullah Saleh on one side, and local residents, Southern Movement militias, and Yemen Army units and militias loyal to Abdrabbuh Mansur Hadi on the other side.

Supporting paragraphs: Battle of Aden Airport Ali Abdullah Saleh
Answer: Yemen