It doesn't take a tennis superfan to know that the state of the sport for the once-powerful American men is in unchartered territory.

For the second straight year, the country that produced John McEnroe, Andre Aggassi and Pete Sampras did not have a representative in the fourth round of the U.S. Open. Both Sam Querrey (below) and John Isner were ousted in the third round. Since the tournament was founded in 1881, these are the only two years in which no American man has failed to advance past the third round.

This is simply the latest nadir in an era full of them for American men. Each year, it seems, the state of the sport becomes worse and worse.

The Americans' poor play has dramatically affected TV ratings and led to the resignation of Patrick McEnroe from his post as the head of player development for the USTA.

And while the results are clear, perhaps most perplexing for those that play and follow the game is the exact cause of this struggle.

"I don't know what's missing," Isner said during the U.S. Open. "I don't focus on that. I just focus on myself. It's not my concern."

Some experts have pointed to the dearth of clay court tournaments for American juniors as a possible root of the issue.

"We need to change the amount we play on clay," Brad Gilbert, a former player, coach and current ESPN analyst, told the Wall Street Journal. "I feel like all the big junior tournaments, everything should be played on clay. That's what the rest of the world plays on in South America and Europe, and we haven't embraced that."

The lack of familiarity with clay has been on display at the French Open where, despite a an encouraging showing this year, Americans seem to struggle more than any other major tournament.

Another potential explanation for the sluggish play of American men is the globalization of the sport. Not only are more and more major tennis tournaments relocating abroad (California, for example, now only has one significant tournament), but about half of all NCAA tennis players are from foreign countries. As the sport expands, one would naturally expect a larger competition pool to challenge the once-dominant Americans.

Finally, and perhaps most difficult to swallow for fans looking for a specific cause, is the notion that these things move in cycles. Europeans are dominating international tennis now, just as Americans did 15 years ago. Perhaps once Novak Djokovic, Rafael Nadal, Roger Federer and Andy Murray age out of the sport a new crop of Americans will take their spots.

Or, maybe, the scope of the question is too big. Rather than focusing on American players as a group, perhaps we should be taking a more micro perspective.

"At the end of the day it's an individual sport," Querrey said. "I don't really care too much. I want all the Americans to do well, but I want them to do well for them."

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