#2 Sir Alex Ferguson’s retirement
Ferguson retired at the end of the 2012-2013 campaign having won the Premier League title. He inspired United to numerous domestic and international titles and left a huge void when he finished his coaching days.
After Sir Alex Ferguson retired, David Moyes was appointed as Ferguson's replacement. Moyes ended up having an unsuccessful reign as Manchester United manager.
Under Moyes, United finished seventh in the league and missed out on Champions League football for the first time in 22 seasons.
United struggled further in the seasons to follow by finishing fourth, fifth and sixth respectively. Ferguson’s retirement proved to be a bitter pill to swallow for United supporters. The club has not won a league title in five seasons since Ferguson left.