As everybody is doubtless already aware, Manchester City and Manchester United face each other at Wembley for the first time this weekend, in the first of two FA Cup semi-finals. To mark this, we are running a week’s worth of articles about football in the city of Manchester, kicking off with an overview of a city rivalry that has intensified in recent years.

Of course, it has never been “just another” match. That isn’t in the nature of that most enduring of football’s creations, the local derby. In the second decade of the twenty-first century, though, the intensity of one of England’s oldest rivalries will hit a new level with the meeting of Manchester City and Manchester United at Wembley, no less, in the first of this weekend’s FA Cup semi-finals. It is a match that will tap into the baser instincts of a city that has been an ever-present hotspot of the national game since the end of the nineteenth century. It’s not a cup final – though with City’s new-found wealth, it may be only a matter of time before this scenario is also realised – but it is a showcase of how one city could come to dominate English football.

Yet Manchester City and Manchester United are not two clubs that have spent the last one hundred and twenty years with their backs turned towards each other. Over the course of their histories, these two clubs have found their histories and their fortunes thoroughly entwined. When one has fallen on hard times, it has been in the full shadow of the other, yet there have also been acts of solidarity that have defied the conventional imagery of the local rivalry as a home for seething hatred and no more. The Manchester derby – and it is not the only one to have done this – can act as a parable for the story of English football, for better and for worse.

It is no coincidence that, while one of the first major financial scandals to rock the game in this country was to hit only Manchester City, Manchester United would become beneficiaries of their ill-doing. City had won the FA Cup in 1904, but had come close to extinction thanks to the after effects of an illegal payment scandal that led to seventeen players being banned and suspended from playing for the club again. Four of those players, including the talismanic Billy Meredith, went on to join United and became part of the first Manchester United team to win the Football League Championship, in 1908.

Yet United were not without their fair share of scandal, either. The club had come close to closure in 1902 (when the largesse of local businessmen, including John Henry Davies, who would go on to serve as a director of the club with great distinction), and in 1915 they were involved in a match-fixing scandal along with Liverpool, which led to four United players being banned for life. One of them, Sandy Turnbull, was one of those transferred to United from City in 1907 and he was killed in action during the First World War. All of those involved were pardoned by the FA in 1919 in recognition of their service to the country, Turnbull posthumously.

The years between the wars saw crowds begin to rise massively. City moved to Maine Road in 1923, but by the end of the 1920s United were in financial trouble again, with James W Gibson taking control of the club in 1931. United spent much of these two divisions bouncing between the two divisions, and City were similarly unpredictable – FA Cup finalists and relegated in 1926, champions in 1937 and relegated the following season. Attendances for matches between the two, however, were rising (68,796 saw United beat City 3-2 in September 1936), but the outbreak of the Second World War saw the two teams in different divisions, with United having been promoted into the First Division in 1938 as City were relegated from it. War, however, brought the clubs back together. When Old Trafford was bombed during a German air raid in March 1941 United moved to Maine Road until the repairs could be carried out, and it took until August of 1949 before they could return home.

That Manchester United rose to become one of the giants of European club football is a given, but even this ascent was tied into their local rivals, as manager Sir Matt Busby spent eight years as a Manchester City player before his playing career was ended by the war. Busby took over the managerial job at Old Trafford in 1945 and his team finished as runners-up in the First Division four times before winning the title in 1952. City, meanwhile, were promoted back into the First Division in 1947, before being relegated and promoted straight back between 1950 and 1952. The Munich Air Disaster, in 1958, also had, its left, in its own way, its mark upon City as well as United. Their former goalkeeper, Frank Swift, who had played over 500 times (including wartime matches) for the club, was amongst the twenty-three that perished in the tragedy.

It took Matt Busby a full decade to rebuild his Manchester United team to a level at which the could win the European Cup, and by the time they did United and City had a strangehold on English football that is often forgotten outside of the city today. Between 1965 and 1968, they each won the league championship twice, with United becoming the first English club to win the European Cup, at Wembley against Benfica in 1968. As the 1970s began, however, it was United that seemed to be in decline and City that seemed the more likely to become the dominant team in the new decade. On top of their two league titles (one of which was a Second Division championship, in 1966), City won the FA Cup in 1969 and the European Cup Winners Cup a year later and, while both were mid-table teams in the league at this point, United seemed in decline, with the decision to replace Busby with Wilf McGuinness proving to be not far short of disastrous. Busby replaced McGuinness again for half a season in 1970 before handing the reins over to Frank O’Farrell, but O’Farrell couldn’t arrest the decline either, and he in turn was replaced by Tommy Docherty at the end of 1972.

That City, playing one of the most iconic of all post-war United players, should have had a hand in United’s ultimate humiliation – relegation from the First Division in 1974 – has become a part of football folklore. It was an accident of design that the two club were playing at Old Trafford on the last day of the 1973/74 season. Less so, perhaps, that Denis Law should have signed for City from United on a free transfer the previous summer. The folklore is well-established – Denis Law back-heeled Manchester United into the Second Division – but it’s far from the entire story of that day. The truth of the matter is that, whilst United needed to win the match to have any chance of staying up, they also needed results to go their way elsewhere. On top of that, even if they had beaten Manchester City and other results had gone their way, they would still have needed to beat Stoke City in their final match of the season.

Perhaps, though, this was the cathartic moment that Manchester United needed. That relegation must have hurt and the pitch invasion which ended that match was an embarrassment to the club. However, this relegation gave Tommy Docherty the excuse that he needed to clear out the dead wood from the club and their stay in the Second Division only lasted for one season. By 1977, they had won the FA Cup again, a year after Manchester City had lifted the League Cup. By the end of the 1970s, however, the balance of power in English football lay in the hands of Liverpool. City spent enormous amounts of money at the end of the 1970s with no significant effect and were relegated again in 1983. They would spend the remainder of the decade bouncing between the top two divisions. In the same season, meanwhile, United won the FA Cup and spent much of the 1980s chasing the coat-tails of both Liverpool and a resurgent Everton.

By the end of the decade, the gap between City and United was well-established, but in September 1989 there was sting for United that might even have changed the destiny of the club. A 5-1 defeat at Maine Road was a shocking result that might have cost Alex Ferguson his job. He clung on, however, and, although they only finished in thirteenth place in the league that season, they won the FA Cup again, beating Crystal Palace after a replay. That, along with a European Cup Winners Cup win the following year would turn out to have been more prophetic for the rest of the decade than may have been apparent at the time. The ushering in of the Premier League in 1992 saw United embark on a upon a run of success that has even managed to eclipse that of Liverpool over the previous two decades. City, meanwhile, slumped to mediocrity and relegation in 1996. Two years later came their ultimate humiliation, a second relegation to what we now know as League One. As Manchester United lifted the European Cup for the first time since 1968, City were celebrating beating Gillingham on penalties in a play-off final at Wembley.

With the new century has come a new sense of priority within English football. The ultimate goal, it could be argued, has become qualification for the Champions League above anything else and, while United have become perennials in this competition, City had a turbulent, if mostly upwardly mobile decade. In 2003, they left Maine Road for the shiny, new City of Manchester Stadium having marked their final derby match at their old home with their first win against United in thirteen years. The following season, their first home match against their rivals at their new ground saw them win by four goals to one. It was the middle of a relative purple patch for City against United (five wins and three draws between November 2002 and March 2008), but United kept winning the trophies, including another Champions League in 2008, while City’s last major trophy became a dimmer and dimmer memory.

By the summer of 2008, City (who had been purchased by Thasksin Shinawatra just over a year earlier) were said to be back on the financial brink, but it was their salvation from this, at the hands of  Sheikh Mansour’s Abu-Dhabi United consortium at the start of the September of that year, which has come to frame the current relationship between the two clubs. Almost immediately, City sought to snatch Dimitar Berbatov from under the noses of United, and since then they have given the impression of seeming to delight in being a thorn in United’s side, with the signing of Carlos Tevez and the subsequent “Welcome to Manchester” billboard placed in the centre of the city being prime examples of their new-found largesse. Even though United’s finances have come under the spotlight since the Glazer take-over in 2005, though, the team has (broadly speaking) kept winning. City’s only win against United since the Mansour take-over came in the semi-finals of the League Cup last year… and United overturned that in the return match before going on to win the final.

The next couple of years could well go on to define the next ten years of the complex relationship between these two clubs, or longer. Who will replace Alex Ferguson when his retirement – which has to come some day – is confirmed? Will the two clubs go head to head in the transfer market? Will Manchester City defy the UEFA Financial Fair Play regulations, or will they come unstuck by them? Throughout their histories, both Manchester City and Manchester United have changed to save themselves and this seems to be ongoing, and these questions will go a long way towards shaping the look and feel of Premier League – and, just possibly, European – football over the next few years or so. Saturday’s FA Cup semi-final will not be the be-all or end-all of either clubs’ season, but to say that local pride will be up for grabs seems likely to be something of an understatement and it will be a spectacle that will demonstrate, if nothing else, the relative current power of football in Manchester.

Follow Twohundredpercent on Twitter here.