There has been a relaxation in ownership rules across the top leagues in Europe since the turn of the century. This has seen wealthy owners with deep pockets arrive on the scene and change the dynamics of the game for good.Three notable examples in this regard are Chelsea, Manchester City and PSG, and more recently AC Milan. These clubs have successfully challenged the old status quo and traditional powerhouses like Real Madrid, Manchester United and Bayern Munich. In the process, they have carved out a niche for themselves, both domestically and in Europe.Unsurprisingly, many quality players have moved clubs since the turn of the century. In fact, there have been 12 transfers worth at least €100 million— an amount unheard of only two decades ago.On that note, here's a look at the ten clubs with the highest spending this century:Note: All numbers and stats as per transfermarkt unless mentioned otherwise.#10 AC Milan - €1.488 billionAC Milan have spent big in the last few years.AC Milan are one of the most storied teams in Italian and European football. However, the Rossoneri haven't won a major title since their 2010-11 Serie A triumph.With key players departing and the team's fortunes plummeting, Milan languished in mid-table mediocrity for a while. However, with Elliott Management taking ownership of the club last year, Milan have been able to attract top talent once again.The Serie A leaders have made a number of big-name signings in the last two decades. However, they have never broken the bank for any player. That is evident in their two top signings of Leonardo Bonucci (€42 million) in 2017-18 and Rui Costa (€41 million) in 2001-02.Transfer News Live@DeadlineDayLiveDEAL DONE: AC Milan have officially confirmed Leonardo Bonucci's transfer. He joins on a 5-year deal for €40m. (Source: @acmilan)5:49 AM · Jul 20, 20171089502DEAL DONE: AC Milan have officially confirmed Leonardo Bonucci's transfer. He joins on a 5-year deal for €40m. (Source: @acmilan) https://t.co/On8J7UBV3eMore recently, Milan dished out €35 million for Krzysztof Piatek (2018-19), €24 million for Franck Kessie (2019-20) and €28.8 million for Fikayo Tomori this summer.#9 Liverpool - €1.622 billionLiverpool are into the Champions League knockouts.Liverpool, much like Milan, have a glorious history, both in Europe and in their domestic league.The Reds have made many high-profile signings in recent years, especially since the arrival of manager Jurgen Klopp. Most of these players have played a key role in Liverpool's resurgence as a force to be reckoned with in England and Europe.Liverpool splurged €84.65 million to land Virgil van Dijk in the 2017 January transfer window, making the Dutchman the world's most expensive defender.Southampton FC@SouthamptonFC#SaintsFC has reached an agreement with #LFC over the transfer of @VirgilvDijk in January. Full statement: sfcne.ws/VVDAgreement11:29 AM · Dec 27, 201734421873#SaintsFC has reached an agreement with #LFC over the transfer of @VirgilvDijk in January. Full statement: sfcne.ws/VVDAgreementThe club-record signing has been a rock at the back for Klopp's men, inspiring them to Champions League and Premier League triumphs in successive seasons.Klopp also signed goalkeeper Alisson (€62.5 million), Mohamed Salah (€42 million), Sadio Mane (€41.2 million), Diogo Jota (€44.7 million) and Fabinho (€45 million). Suffice to say, all these players have made Liverpool the team they are today.The Reds recently became the first English team to win all six group stage games in a Champions League season. They are currently second in this season's Premier League table.#8 PSG - €1.646 billionPSG have become a force to be reckoned with this summer.PSG made the news this summer when they made a spate of high-profile signings. The Ligue 1 giants snapped up Lionel Messi, Sergio Ramos, Gianluigi Donnarumma and Georginio Wijnaldum on free transfers. That made for one of the greatest transfer windows by any club in the game's history.However, the QSI-owned club haven't hesitated to splurge in order to land their top targets. Only four years ago, PSG shelled out a staggering €222 million to bring Neymar to the Parc des Princes.B/R Football@brfootballOn this day in 2017, PSG signed Neymar from Barcelona for €222M/$264M, making him the most expensive transfer ever 🤑10:54 AM · Aug 3, 2021241701615On this day in 2017, PSG signed Neymar from Barcelona for €222M/$264M, making him the most expensive transfer ever 🤑 https://t.co/uUz7mhyYxFThat made the Brazilian the world's most expensive transfer of all time. Only a year later, they parted with €145 million to land Kylian Mbappe. Both players, particularly the latter, have proved to be highly successful signings.Other big-money PSG transfers this decade include their record scorer Edinson Cavani (€64.5 million), Angel Di Maria (€63 million), and more recently Achraf Hakimi (€60 million).It remains to be seen if the expensively assembled star-studded team can conquer Europe this season, as their Ligue 1 triumph is all but a given.#7 Inter Milan - €1.772 billionInter Milan have fared well despite their recent financial woes.Serie A holders Inter Milan have fared pretty well despite the exit of their manager Antonio Conte, star striker Romelu Lukaku and right-back Achraf Hakimi this summer.Despite their recent financial woes, the Nerazzurri are flying high in Serie A this season. They currently sit only a point behind league leaders AC Milan. In the Champions League, Inter have reached the Round of 16, finishing behind group winners Real Madrid.The Nerazzurri have only started splurging in the last few years. They never went beyond €46.8 million (Christian Vieri, 1999-00) before they dished out €74 million to bring Romelu Lukaku in the summer of 2019. A year later, Inter spent €43 million on Achraf Hakimi, and went on to win their first league title in 11 years.Other notable Inter signings during the last two decades include Hernan Crespo (€40 million, 2002-03), Milan Skriniar (€34 million, 2017-18), Nicolo Barrella (€32.5 million, 2019-20) and Francesco Toldo (€26.5 million, 2001-02)