The club's most successful period was from 1968 to 1970, when they won the League Championship, FA Cup, League Cup and European Cup Winners' Cup, under the management team of Joe Mercer and Malcolm Allison. After losing the 1981 FA Cup Final, the club went through a period of decline, culminating in relegation to the third tier of English football for the only time in their history in 1998. Having regained their Premier League status in the early 2000s, the club were purchased in 2008 by Abu Dhabi United Group for £210 million. Since 2011, the club have won five major honours, including the Premier League in 2012 and 2014.
By 2016–17, Manchester City had the fifth-highest revenue in the footballing world with an annual revenue of €527.7 million. In 2017, Forbes magazine estimated they were the world's fifth-most valuable football club, worth US$2.08 billion. In 2015, a 13.79% stake purchase for the club's parent company, City Football Group (CFG), by the CITIC Group for £265 million valued the entity at $3 billion.
City gained their first honours by winning the Second Division in 1899; with it came promotion to the highest level in English football, the First Division. They went on to claim their first major honour on 23 April 1904, beating Bolton Wanderers 1–0 at Crystal Palace to win the FA Cup; City narrowly missed out on a League and Cup double that season after finishing runners-up in the League but City became the first club in Manchester to win a major honour. In the seasons following the FA Cup triumph, the club was dogged by allegations of financial irregularities, culminating in the suspension of seventeen players in 1906, including captain Billy Meredith, who subsequently moved across town to Manchester United. A fire at Hyde Road destroyed the main stand in 1920, and in 1923 the club moved to their new purpose-built stadium at Maine Road in Moss Side.
In the 1930s, Manchester City reached two consecutive FA Cup finals, losing to Everton in 1933, before claiming the Cup by beating Portsmouth in 1934. During the 1934 cup run, Manchester City broke the record for the highest home attendance of any club in English football history, as 84,569 fans packed Maine Road for a sixth round FA Cup tie against Stoke City in 1934 – a record which still stands to this day. The club won the First Division title for the first time in 1937, but were relegated the following season, despite scoring more goals than any other team in the division. Twenty years later, a City team inspired by a tactical system known as the Revie Plan reached consecutive FA Cup finals again, in 1955 and 1956; just as in the 1930s, they lost the first one, to Newcastle United, and won the second. The 1956 final, in which Manchester City beat Birmingham City 3–1, is one of the most famous finals of all-time, and is remembered for City goalkeeper Bert Trautmann continuing to play on after unknowingly breaking his neck.
After relegation to the Second Division in 1963, the future looked bleak with a record low home attendance of 8,015 against Swindon Town in January 1965. In the summer of 1965, the management team of Joe Mercer and Malcolm Allison was appointed. In the first season under Mercer, City won the Second Division title and made important signings in Mike Summerbee and Colin Bell. Two seasons later, in 1967–68, Manchester City claimed the League Championship for the second time, clinching the title on the final day of the season with a 4–3 win at Newcastle United and beating their close neighbours Manchester United into second place. Further trophies followed: City won the FA Cup in 1969, before achieving European success by winning the European Cup Winners' Cup in 1970, beating Górnik Zabrze 2–1 in Vienna. City also won the League Cup that season, becoming the second English team to win a European trophy and a domestic trophy in the same season.