It is difficult to remember a time before Barcelona was an all-conquering force, and Pep Guardiola was hailed as a messiah amongst managers. The Catalan team has changed soccer as we know it both in terms of the way that they play, and the way that opponents need to play to stop them. Teams have been built from the ground up specifically with the idea of stopping Barcelona (Jose Mourinho’s Real Madrid), academies have been set-up specifically to imitate La Masia (Manchester City), and their tactical formations have caught the eye of countless teams (Luis Enrique’s Roma, Brendan Rodgers’ Swansea City and early Liverpool teams, just to name a few).

This is in no way a eulogy, Barcelona is still the best team on the planet and will probably be so for many seasons (until England figures out how to use its economic clout). But Barca has changed. This is through necessity, one cannot keep expecting Messi and Iniesta, Xavi, and Busquets to roll off the academy production line in batches. And if you buy players, even great players such as Luis Suarez and Neymar, styles will have to be altered to accommodate them.

Barcelona now do not have any sort of sterile dominance, the pointless possession that was highlighted as perhaps their only flaw under Pep Guardiola. They move the ball quickly, hitting the feet of their magical South American forward line or sending balls behind the defense for somebody to run onto.

Of course, as the juggernaut kept rolling, people started to understand the point of what Pep’s “sterile” dominance really was, as much a defensive strategy as an offensive one. If you have the ball, you are the only person that can score, it’s a fundamental truth of the game. Why work on a defensive shape when your offensive shape is your defense?

But it is neither the tiki-taka passing nor the famous diagonal from Xavi to Dani Alves that is the greatest legacy of Pep. I would argue that it’s not the 4-3-3 either, teams have long known that the way to control possession is to outnumber the opposition in midfield. At this point the Barcelona academy is basically an intrinsic resource, even their top coaches can’t replicate the success at other clubs with greater resources (ask City). No, Guardiola’s greatest achievement has to be the reinvention of the three-man backline, even when he used a four man backline.

A three man defense is an odd thing, it was very useful in the 1990s when 4-4-2 was in vogue because a 3-5-2 had two forwards and outnumbered the opposition in midfield, while still having a center back in reserve to be a sweeper. When 4-3-3, 4-2-3-1, and forwards playing as false nines became more popular (partly because the three man defense shut down the 4-4-2 to such an extent), it was not so useful.

It comes up every now and then as a tactical curveball in England, and has remained popular in Italy due to its ability to shift to a 5-3-2 and completely close down a game. However Guardiola was the person who brought the three man defense to the modern age, and proved that you don’t even need to line up with a 3-5-2 or 3-4-3 to do it.

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How was his 4-3-3 a three man backline? It was due to Sergio Busquets completely reinventing the role that Guardiola had made his own during his own playing days. In a 4-3-3 with two technically gifted and attacking full-backs (especially Alves at right back), and two wingers who wanted to move inside (Messi and Pedro, maybe Thierry Henry or David Villa), the natural solution to keep width during Barcelona’s offensive moves was to push the full-backs up.

Width was especially key for Barcelona because of the way they probed through recycling possession, getting the ball out wide and giving the players in the center time to drift away from their marker or start a run before it went back in. The downside? Carles Puyol and Gerard Pique would be left completely alone, with no Makelele type in front of them to scythe down opponents on the break.

The genius of Guardiola lay in realizing where he had a surplus and shortage of resources during this phase of play. Recognizing that Busquets was not adding anything in the opposition third of the pitch, where there were already eight of his colleagues buzzing around, Guardiola directed him to drop in between Puyol and Pique, ensuring defensive balance was restored. If somebody sprinted behind Alves’ advanced position, Puyol could now go and cover confidently in the knowledge that there were two people defending balls into the box behind him.

Why this development is so important is the fact that almost any team trying to break down a stubborn opponent can do it. Obviously not to the same extent and success because of differences in personnel, but Busquets’ move also redefined how a center-back is supposed to play in a top team that dominates the ball.

Liverpool’s team for the League Cup final featured Lucas Leiva playing center-back. Emre Can has also played center-back for Liverpool, and it’s because they were comfortable filling that role as holding midfielders first. Their vision and reading of the game was deemed more important than being big and burly.

Manchester United used to use Michael Carrick as their Sergio Busquets, and now they too play him as center-back in a pinch. Gary Cahill went from unfashionable Bolton to Chelsea specifically because of his comfort in playing high up the field (remember this was Villas-Boas’ Chelsea).

And as with competition in any industry, once you chance upon something that increases competitive advantage, others will try and erode it. Center-backs that are good on the ball and have good passing vision, but who aren’t strong in the air or muscular has led to a resurgence of bullying number nines. Teams like Watford and Leicester who play a rough and ready 4-4-2 have had success precisely because big teams who imitated Guardiola have forgotten how to deal with pure power. The tactical developments caused by this Barcelona team never cease to amaze.