Jurgen Klopp's Arrival Heaps Pressure on Manchester United and Louis Van Gaal

Jurgen Klopp's arrival as Liverpool manager will strengthen the Premier League and provide stiff competition for Louis van Gaal and Manchester United at a time when they can ill afford any additional challenges.

The spectre of doing a Liverpool has loomed over Old Trafford since the retirement of Sir Alex Ferguson and the implosion that followed David Moyes' ill-fated attempt to replace him.

Liverpool's fate seemed inextricably linked to United's—their success in the 1970s and '80s casting a shadow down the length of the M62. Their dominance collapsed just as United's began, the shadow changed direction, and they have not won the league since 1990.

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When United won their first league title for 26 years in 1993, it seemed unimaginable Liverpool would not have won another by now. There was a tangible sense of dread among United fans when, in the season after Sir Alex retired, Liverpool came within a whisker of ending that drought.

Since the Moyes season of 2013-14, Liverpool's fate has loomed over United like a warning from history. Football has changed a lot, and United have an advantage in wealth Liverpool did not have at the beginning of the '90s, but nonetheless, the title has looked a long way off since Ferguson retired.

Indeed, such were Moyes' struggles during his season in charge that plenty of jealous glances were stolen in the direction of the then-Borussia Dortmund manager.

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He had taken his side to success in Germany and to a Champions League final playing a brand of football that was reminiscent of Sir Alex's best sides, as observed by Greg Johnson in the Mirror in April 2014. 

Eventually, of course, perhaps tired of Bayern Munich buying his best players and walking away with the league, the Dortmund dream deflated and Klopp walked away.

The timing—for those United fans who saw Klopp as an ideal fit for the club—could not have been worse. He was absolutely unavailable when Darren Lewis and Martin Lipton of the Mirror reported—also in April 2014—that Klopp was "the first choice of the Old Trafford hierarchy."

He did not become available until after Van Gaal was in post at United, and by that point, there was no pressing need for United to consider a new direction.

Thus, Klopp has ended up at United's bitterest rivals, and given his track record and the obvious fit between his romance-driven approach and Liverpool's culture, there seems a reasonable chance he will succeed.

Of course, the financial realities of the Premier League remain in place, but there will certainly be upward pressure applied to United from Liverpool's new setup.

With the humbling, expectation-resetting defeat at Arsenal last time out, United's current place in the pecking order is unclear. Last season's push for the top four ended with the bare minimum targets being achieved, but this season's goals should surely be loftier.

Even setting aside the expectation that United should once again be challenging at the top of the Premier League, setting sights higher than fourth place has become more important than ever. English clubs' recent lack of European success has affected the feeling of certainty that each of the Premier League's top four will get a crack at the Champions League.

As Gerard Brand reported for Sky Sports, in terms of UEFA coefficients, "Italy could potentially surpass England in the near future."

Brand broke down the various potential scenarios in his article, but the short version is that there is a reasonable likelihood only the top three in the Premier League will gain a place in the Champions League come the 2017/18 season.

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That, of course, would mean that Klopp's challenge at Liverpool would be even greater than it already is. From United's perspective, though, it means they cannot afford another serious challenger as they look to avoid the kind of 20-year dip history teaches us can befall a club once they lose their place at the summit.

United will be desperate to avoid doing a Liverpool as Klopp looks to finally bring Liverpool back to the top, a place that was United's for so long.