History of Vietnam since 1945 unstable as no government could keep power for long. There were more coups, often more than one every year. The Communist-run Viet Cong expanded their operation and scored some significant military victories during this period. In 1965, US President Lyndon Johnson sent troops to South Vietnam to secure the country and started to bomb North Vietnam, assuming that if South Vietnam fell to the Communists, other countries in the Southeast Asia would follow, in accordance with the domino theory. Other US allies, such as Australia, New Zealand, South Korea, Thailand, the Philippines, and Taiwan also sent troops to South Vietnam.
What Happened to Us a "mid-tempo duet ballad" which signifies Mauboy's strength as a global player. On 21 March 2011, "What Happened to Us" debuted at number 30 on the ARIA Singles Chart, and peaked at number 14 the following week. The song was certified platinum by the Australian Recording Industry Association (ARIA), for selling 70,000 copies. "What Happened to Us" spent a total of ten weeks in the ARIA top fifty. The music video for the song was shot in the Elizabeth Bay House in Sydney on 26 November 2010. The video was shot during Sean's visit to Australia for the Summerbeatz tour.