The U.S. Clay Court Championships, a men’s tennis tournament that ended Sunday in Houston, signaled something beyond the transition from the hard-court season to clay.

It marked the end of the tennis tours’ two-month U.S. swing, which included six tournaments, featuring two of the biggest tournaments outside of the four Grand Slam events — the BNP Paribas Open in Indian Wells, California, and the Miami Open.

As the ATP and WTA tours shift to the red clay and grass courts of Europe, the next major events in the United States will not come until the hard-court season in July in the lead-up to the U.S. Open.

And after the U.S. Open wraps up in early September, the tennis tours depart again, spending much of the end of the season in Asia.

U.S. tennis fans used to have more options. In 1990, 24 of 55 events on the women’s tour, the WTA, were in the United States. But with the sale of the Connecticut Open in New Haven this year, only seven of 55 WTA events on the 2019 calendar are on U.S. soil. Five of those seven are joint events with men, including the U.S. Open, Indian Wells and Miami.

On the men’s side, 16 of 77 worldwide ATP events in 1990 took place in the U.S. This year, 11 of 63 will be.

At one time, both the men’s and women’s year-end tour finals were played at New York’s Madison Square Garden, but now the men’s event takes place in London and the women’s is in Shenzhen, China. Smaller tournaments in the U.S. have had trouble selling enough tickets and sponsorships to stay financially viable. And there was even some concern that the Miami Open, which was looking for a new stadium site last year, might be lured out of the country.

“I don’t think that we will ever become a U.S.-centric tour again,” said Steve Simon, the chief executive of the WTA. “I think there’s certainly room for growth for a couple more events, but I think the growth will be in that the events that are here in the States will continue to get bigger. But I do think that we have moved to having a global footprint versus being focused primarily in one country.”

Simon said that the WTA planned to introduce two new events in the U.S., one beginning this year and another in 2020, both of which will take place the week before the U.S. Open. The location of the 2019 tournament, which would bring the total of WTA events in the U.S. to eight, is expected to be announced in May.

The decline in the number of U.S. tournaments over the past three decades corresponds with the decline in the number of Americans atop the world rankings — especially on the men’s side — and the growth of tennis in Europe and Asia.

In December 1990, seven of the top 20 men’s players in the world were Americans, including household names like Andre Agassi, Pete Sampras, Michael Chang and John McEnroe.

The current rankings include only John Isner at No. 10 among the top 20, followed by Frances Tiafoe at No. 29. They are the only American men in the top 50, and no American man has won a Grand Slam event since Andy Roddick at the U.S. Open in 2003. Since then, Europeans, led by Switzerland’s Roger Federer, Spain’s Rafael Nadal and Serbia’s Novak Djokovic, have won 59 of the 61 major titles.

Women’s tournaments fled the U.S. even though Serena and Venus Williams were dominant players over the past 20 years and are the reason many current American players took up tennis.

With more than half of the world’s population in Asia, the WTA looked to that continent as a pillar of growth, said Stacey Allaster, the chief executive of professional tennis for the U.S. Tennis Association and a former leader of the WTA.

In 1990, only four WTA tournaments were staged in Asia. This season there are 11 in China alone, part of a tennis boom fueled by the success of Li Na.

“I don’t think it’s about the quantity of events” in the U.S., Allaster said. “We need successful events.”

And for smaller tournaments, being successful can be tough.

When Anne Worcester, the tournament director of the Connecticut Open, realized the tournament was no longer economically viable, she attempted to find a new title sponsor for the event in New Haven.

She considered offers from various U.S. cities, but she ultimately sold the tournament to the highest bidder, APG, a sports and entertainment company with a strong footprint in Asia. This year, the tournament, which used to be held the week before the U.S. Open, will be in Zhengzhou, China, the week after the Open.

“It has been very emotional to let go of something that I’ve birthed and nurtured for 21 years,” said Worcester, who was the chief executive of the WTA from 1994 to 1998. “My kids are 21 and 23, so it was really like having a third child. But the economics were so clear and because I was leading the charge to secure a title sponsor as well as cultivate bidders around the world, I just saw the writing on the wall. As much as our board didn’t want to sell, there was just no choice.”

Worcester said it was hard to sell tickets and sponsorships in part because there were fewer U.S. stars to promote. The Connecticut Open in recent years has featured European stars like Simona Halep, Petra Kvitova and Caroline Wozniacki.

“In this global sport of tennis, it’s not easy to promote non-Americans,” Worcester said. “Americans want to see Americans.”

The bleeding may have stopped on WTA events leaving the United States. Interest was high in the New Haven event, Worcester said, because global bidders knew that a tournament of its caliber would not be sold again for a long time.

Patrick McEnroe, an ESPN analyst, said that the major American events like the U.S. Open, Indian Wells, Miami and Cincinnati are stronger and more popular than ever, but that the lower-level events like the New York Open may continue to face difficulties.

“To me, the only way that those can get back to being consistently viable year after year,” he said, “is if at the top we have more American tennis players close to the top that have personality that can sell some tickets.”