Five things to know about Major League Soccer

Founded in 1993 as part of US Soccer's successful hosting of the 1994 World Cup, Major League Soccer kicked off its first season in 1996 with 10 teams.

Now into its 22nd season, the competition has expanded beyond all recognition. It now comprises 23 teams spread across North America -- 20 in the United States and three in Canada -- and this season welcomed an expansion side, Los Angeles FC. Miami and Nashville's acceptance will take the league to 25 teams; the league will ultimately expand to 28.

In keeping with the other major professional sports leagues in North America, the MLS is a closed competition with no promotion or relegation. A regular season split into Eastern and Western Conferences kicks off in March each year and is followed by a series of playoffs culminating in the MLS Cup final, usually held in December.

SPRINKLING STARDUST

Major League Soccer was given a jolt of international recognition when the Designated Player Rule -- nicknamed the Beckham Rule -- became effective as part of the salary cap regime in 2007.

This regulation allowed every MLS franchise the freedom to sign a player who was not constrained by the salary cap rules, enabling clubs to offer higher wages to players from around the world.

Beckham's arrival was followed by a steady stream of high-profile international stars at the tail-end of their careers, which included Thierry Henry (New York Red Bulls), Kaka (Orlando), Didier Drogba (Montreal), Andrea Pirlo and David Villa (New York City), Steven Gerrard (Los Angeles Galaxy), Frank Lampard (New York City) and Bastian Schweinsteiger (Chicago Fire).

In recent years as the league has matured, clubs have moved away from hiring older players, instead mining for up-and-coming talent in South America.

Ibrahimovic's arrival bucks that trend, although the Swede has not been signed on a designated player contract, a factor which has limited his salary to around $1.5 million a season -- a fraction of his Manchester United wages.

RISING ATTENDANCES

Major League Soccer is now one of the best attended football leagues in the world, attracting an average gate of more than 22,000 fans per game in 2017 for the first time in history. According to MLS figures, that put it ahead of France's Ligue 1 and Italy's Serie A for average crowd sizes.

Expansion side Atlanta United FC attracted a record crowd of 71,874 for their game against Toronto in October at the Mercedes-Benz Stadium. The Seattle Sounders consistently draw crowds of more than 40,000 to their home games, averaging 42,600 in 2016.

Beckham's arrival in 2007 helped boost average attendances by 8.2 percent, at 16,770 per game. Though that number fell in 2008 and 2009, gates have risen steadily ever since, jumping by as much as 12.7 percent in 2015 following the excitement caused by the 2014 World Cup.

Television remains a harder nut to crack, however. An average of 272,000 viewers tuned in on ESPN for regular-season games in 2017, some distance of the ratings giant of the NFL, which averages around 14.9 million viewers per game.

A NEW WORLD

Ibrahimovic, like many overseas stars before him, could be in for a culture shock when he gets down to work in MLS after more than a decade spent gracing some of European football's most iconic arenas.

Among the peculiarities of the MLS are strict rules regarding team travel. Designed to create parity, teams are allowed to charter private planes for no more than four legs of travel throughout the season.

This means teams criss-crossing the United States for league matches often have to fly in coach class on commercial passenger jets, a far cry from the pampered luxury Ibrahimovic will have been used to during his spells with the likes of AC Milan, Barcelona, PSG and Manchester United.

Ibrahimovic will also have to get used to playing many games on artificial turf. That could be significant for Ibrahimovic, who is recovering from a serious knee injury.

Some studies have suggested athletes are at a greater risk of injury playing on artificial turf.

WORLD CUP FALL-OUT?

The rapid rise of football in the United States suffered a severe jolt last year when the men's national team failed to qualify for the 2018 World Cup in a shocking upset.

So far however there is no sign that the setback has impacted MLS's burgeoning popularity, with strong attendances a feature of the first few weeks of competition since the 2018 season kicked off earlier this month.

The World Cup has been a consistent engine of growth for MLS. In each of the MLS seasons following the 2006, 2010 and 2014 World Cups, attendances spiked as new fans flocked to stadiums, with crowd numbers rising dramatically.

And football in North America could well benefit from another jolt of energy looming on the horizon, with a joint United States-Canada-Mexico bid for the 2026 World Cup considered to be the front-runner to win a vote for the tournament, which this year will be held in Russia from June 14-July 15.