The stunning and unexpected trade that sent Edmonton Oilers superstar Wayne Gretzky to the Los Angeles Kings 25 years ago today was a landmark event for the NHL that changed the entire landscape of the sport in the United States.

It started an immediate explosion of interest and growth in the NHL throughout America; the impact of the deal is still being felt today and will continue to affect the league well into the future.

Without Gretzky's move to Hollywood in 1988, the league may not have been able to successfully expand to nontraditional American hockey markets in western and southern states throughout the early-to-mid 1990s.

His popularity, combined with the fact that he played in Los Angeles, put the NHL on national television, made headlines throughout the United States and had a gigantic influence on the sport's growth in new markets.

After the WHA merger in 1979, the league had 21 teams and the Kings were the only American franchise located west of Minnesota.

Shortly after Gretzky boosted the popularity of hockey as a member of the Kings, the NHL added five expansion clubs, including two in Florida (Tampa Bay Lightning in 1992-93 and Florida Panthers in 1993-94) and two more in California (San Jose Sharks in 1991-92 and Mighty Ducks of Anaheim in 1993-94).

In 2013, 23 of the NHL's 30 teams are in American cities. Ten of those U.S. franchises came into existence (including teams that relocated) after the Gretzky trade and five of them have won the Stanley Cup (Kings, Ducks, Hurricanes, Lightning and Avalanche).

Without the Gretzky trade, it's not difficult to make the argument that franchises such as the Ducks, Panthers and Coyotes wouldn't exist because the interest in hockey throughout Western and Sun Belt markets would have been significantly lower in the 1990s.

Gretzky's influence also helped the NHL excel in markets it had previously failed in before his trade to Los Angeles, including the Bay Area and Denver.

When the Gretzky's Kings played preseason games, most of them were on the road in markets where the NHL didn't have a team and could possibly expand to.

This was an effort to familiarize casual fans with the excitement of pro hockey and the brilliance of Gretzky, and for the most part, the strategy was effective. Even if fans weren't too familiar with the sport, they knew who Gretzky was and how he compared to other great athletes such as Michael Jordan.

Even though the Kings winning their first Stanley Cup in 2011-12 could be seen as a culmination of Gretzky's work in Los Angeles, his impact on hockey in California and other western/southern states will continue to be felt for many years.

California had produced five NHL players before 1988. That number now stands at 27, with recent first-round picks such as Jonathon Blum (2007), Beau Bennett (2010) and Emerson Etem (2010) all learning to play hockey in the Sunshine State. 

During the same season that the Kings won the Stanley Cup, a team based in Los Angeles won the Quebec International Pee Wee Tournament, which is one of the most respected hockey competitions in the world. The idea of a California team winning this tournament would have been laughable prior to the Gretzky trade.

"I remember one time watching the game on TV and the L.A. Kings had 18,500 and the Anaheim Ducks had 17,000 people there, and 35,000 people in California going to an NHL game the same night and I said, 'you know hockey's come a long way,'" Gretzky told NHL.com earlier this year. "My timing of going to L.A. just happened to come at the right time."

According to Chris Peters from The United States of Hockey, the number of people participating in hockey in the state of California skyrocketed from 4,483 in 1990-91 to 20,204 by the end of the 2009-10 season.

Peters writes:

Wayne Gretzky coming to LA had a huge impact on hockey in California. In 1995-96, Gretzky’s last season in LA, California’s hockey playing population had already ballooned to 15,537 (221.7% growth from 1991).

According to Peters, 15 states have seen participation in hockey rise 150 percent or more from 1991 through 2010, headlined by nontraditional hockey states such as Texas (1,156.8 percent), Florida (804.7 percent) and North Carolina (502.6 percent).

In the 2000s, 564 American-born players were drafted to NHL teams, the most of any decade in league history. Many of those players grew up watching Gretzky.

The impact of the Gretzky trade is also being felt on the international stage.

The United States team at the 2010 World Junior Championships included 10 players from nontraditional hockey markets. The group of Americans who won the gold medal at the 2013 World Junior Championships in Russia featured players from 13 different states. Two of the team's best players, forward Rocco Grimaldi and defenseman Seth Jones, are from California and Texas, respectively.

Hockey has truly become a national game in America following the Gretzky trade. There are top-tier players learning the game in all types of markets, not just the traditional hockey hotbeds of Massachusetts, Michigan, Minnesota and New York.

The NHL probably would have expanded into western and southern American markets sooner or later, whether Gretzky was traded or finished his career in Edmonton. But the trade expedited the process and it made it easier for the NHL to add teams and grow the game.

By gaining a wider footprint in the United States with teams in almost every major market, thanks in large part to Gretzky's impact on hockey's growth, the league was able to popularize the sport to a level that would earn it a record 10-year, $2 billion national television contract with NBC Sports in 2011.

If Gretzky's trade never happened, it's hard to imagine the NHL having this lucrative of a U.S. television deal right now because the popularity of hockey in major western markets (Los Angeles, Bay Area, Phoenix, etc.) wouldn't be strong enough.

Each major North American sports league has been impacted by blockbuster trades that changed the fortunes of certain franchises, but no deal in any sport has made a larger impact on its growth than the Gretzky trade 25 years ago.

As the NHL increases its popularity and becomes a bigger business with at least seven more years of labor peace on the horizon, we will continue to witness the influence that Gretzky had on the hockey culture in nontraditional markets and how he positively impacted the sport in the United States.

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Nicholas Goss is an NHL Lead Writer at Bleacher Report. He was a credentialed writer at the 2011 and 2013 Stanley Cup Final, as well as the 2013 NHL draft.