Recent summer transfer windows have formed some of the biggest turning points in Manchester City's history.

In summer 2007, Sven Goran-Erkisson spent £46million of Thaksin Shinawatra's funds on a cohort of players he'd only ever seen on video tape, including Elano, Rolando Bianchi, Verdan Corluka, Gelson Fernandes and Martin Petrov, opening the era of affluence at the Etihad and leading to their then-second highest finish in Premier League history.

A year later, the club smashed their record transfer fee with a £33million swoop for Robinho, alongside Pablo Zabaleta and Vincent Kompany, as Sheik fortunes arrived from Abu Dhabi.

Summer 2010 saw the acquisitions of Yaya Toure, David Silva, Aleksander Kolorov, James Milner and Edin Dzeko, whilst £38million man Sergio Aguero arrived in 2011. Less than twelve months later, City won their first ever Premier League title.

Set to enter the next transfer window trophy-less for 2014/15 however, with fresh blood desperately required both on the pitch and in the dugout, the coming summer could be Manchester City's most important yet. As one era ends and other begins, every appointment, signing and decision will have huge ramifications on City's bid to become one of Europe's most dominant forces. Get it wrong, and they'll be thrown into purgatorial dormancy.

Although Manuel Pellegrini has his fans throughout the City support, few dispute that the team has slowly regressed under his leadership. They ended last season in a somewhat laboured fashion, albeit with a second Premier League title, and the Chilean's over-optimistic naivety, his stubborn insistence upon an open and expansive 4-4-2 formation, has once again cost the Sky Blues dearly in Europe - the ultimate platform for success in the eyes of the Sheik owners - after crashing out to Barcelona in midweek.

A manager who had previously won just a single European trophy - the 2004 Intertoto Cup - before arriving at the Etihad, City need a true managerial heavyweight, capable of not only providing instant success but most crucially rebuilding a star-studded squad from the ground up. Fans only need consider the misfortunes of rivals Manchester United under David Moyes last season however, to realise how detrimental the wrong appointment in such a scenario can quickly prove to be.

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After all, the current City starting Xi is slowly but surely coming to the end of its natural lifespan. Their average squad age of 29 is the oldest in the Premiership by almost a year and over the course of this season, the balance between quality and industry has skewed towards the former. Although Yaya Toure, David Silva and Samir Nasri are all fantastic technicians and creators, their lackadaisical approach to defending continues to cost City in the big games. They haven't beaten any of the Premier League's top four from 2013/14 since Liverpool in August - their second game of the campaign.

Likewise, City's inability to put up a worthy title defence for the second time speaks volumes about the mentality of the players. Under two different managers they've failed to retain the English crown, and the 1-0 defeat to Burnley last weekend provides the perfect case in point; when it comes to the less glamorous occasions, City just aren't up for the fight. They've become style over substance.

It's time for somebody to leave the party and make way for new stars. The only alternative is replacing the majority of the first team simultaneously in a couple of seasons' time, an even graver risk to take. Speculation this morning suggests that could well be the high earning Yaya Toure. Still a great player, but without the superfluous supply of goals from prior campaigns, difficult to justify at £240k per-week.

Of course, it's a task monumentally easier said. The board will be looking around Europe at the likes of Raheem Sterling, Ross Barkley, Paolo Dybala, Raphael Varane, Alexandre Lacazette and many more youngsters with the potential to flourish into worldly stars.

But they've been here before; Jack Rodwell, Matija Nastasic, Mario Balotelli, and Adam Johnson were all tipped for greatness and never delivered. The harrowing difference now is the diminishing safety net of proven stars to fall back on - some, like Toure, heading for the exit, others, like Zabaleta, naturally declining with age - and the fear of destroying a project overnight that City's Sheiks have poured billions into already.

That summarises perfectly why the coming summer is so important for City; it will mark the beginning of the end for some, the absolute end for a few, and a tectonic shift in the course of the most expensively assembled empire in the Premier League for all.

City need signings that can underpin their squad for the next decade and a manager guaranteeing success. That's a hell of a lot to look for in a single summer; mistakes, rather worryingly, seem inevitable.

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