Defenders used to be an afterthought. When transfer budgets were finalized and lists of targets compiled, reinforcing the back line was one of the lesser priorities. The big money went on goal scorers and thrusting midfielders.
Virgil van Dijk's £75 million move from Southampton to Liverpool illustrates a change in emphasis. Centre-halves and full-backs are in demand. Eyebrows were raised last year when Manchester City paid £47.5m for John Stones. Since then, Pep Guardiola has spent more than £100 million on full-backs: £50m to Tottenham Hotspur for Kyle Walker and £52m more to Monaco for Benjamin Mendy. The Van Dijk deal ups the ante, not only in the Premier League but across Europe.
It has worked for City. Even though Mendy suffered a long-term injury in September, Guardiola's side have conceded the fewest goals in the Premier League (12). Their high-octane attack has drawn the most plaudits, but City are much more solid than they were last season.
On Merseyside, Jurgen Klopp has crafted a forward line that is almost as effective as City's strike force. They are the two most exciting teams in the division. Unlike the league leaders, Liverpool have been leaking goals -- many of them avoidable.
Liverpool's defensive problems predate Klopp. They have struggled to find adequate reinforcements at the back. Dejan Lovren (£20m) and Alberto Moreno (£12m) were relatively expensive in 2014, but so far their Anfield careers have been only memorable for their litany of errors. Attempts to rebuild on the cheap -- Ragnar Klavan (£4.2m), Joel Matip (free transfer) -- have proved little more successful. Anfield's recruiting department has either struggled to sign effective defenders or successive managers have been unable to fashion them into a coherent unit.
Fault lies in both areas. Signing Lovren from Southampton appeared to be a good move. The Croatia international was impressive during his spell at St Mary's but has underperformed badly after his move north. The 28-year-old expected to get more cover from the Liverpool midfield and found himself unprotected too often in his early days at Anfield. His confidence was undermined and he has never recovered.
There were high hopes that Lovren would solve many of Liverpool's defensive issues when he signed. Van Dijk will be burdened by even weightier expectations. The Dutchman will improve Klopp's back line but will not provide a cure for all the rearguard's problems.
The flawed and vulnerable Moreno remains first choice at left-back -- Andy Robertson is below the Spaniard in the pecking order -- and Klopp will mix and match to find the best partnership at centre-half. The Liverpool manager has options at right-back with Trent Alexander-Arnold having the potential to keep Nathaniel Clyne out of the side, but Liverpool's frailties are more widespread than the back four.
Van Dijk may be no more comfortable with the midfield than Lovren. Liverpool lack dynamism in the areas in front of the central defenders. There are also severe trust issues with Simon Mignolet, a goalkeeper who does not communicate with the outfield players effectively enough or dominate his area.
The signing of Van Dijk is a big step forward for Klopp, though. It is a clear statement of intent that the club are prepared to spend so much on a player that the manager wanted badly. It is even more satisfying for the club that Liverpool beat City to the 26-year-old's signature.
Behind the scenes at Anfield there is resentment about the growing power at the Etihad. Everton and Manchester United have been Liverpool's traditional rivals, but internally City are seen as the adversaries of the future. Their wealth, infrastructure and recruitment methods have caused animosity among some of their peers, and Liverpool take pleasure in any victory over City, on or off the pitch.
Fenway Sports Group, Liverpool's owners, are prepared to spend big to fulfill their ambitions. The Boston-based group do not need to sell to finance the Van Dijk deal. They are keen to support Klopp and bring in high-priced players when necessary.
They would also prefer to retain Philippe Coutinho. The Brazilian has been heavily courted by Barcelona since the summer and is unlikely to leave Anfield in January. A summer exit is probable, but not because Liverpool need the money. The 25-year-old is very keen to go to the Nou Camp, and given that Klopp has a wealth of options up front, Liverpool are unlikely to keep a player who is desperate to leave.
Van Dijk will add strength and depth to the defence. He is an expensive building block rather than a ready-made answer to the team's deficiencies. Naby Kieta's arrival from RB Leipzig in the summer will improve the midfield, too.
Liverpool are in the process of building a team that they believe will give Klopp the chance to compete with the best. They may have to spend even more to overhaul the defence to the manager's satisfaction.