More people are traveling the world than ever. But the number coming to America is dropping.

Travelers can't get enough of globe-trotting. But have they had enough of the United States?

According to the World Tourism Organization, a United Nations agency, the number of international tourist arrivals around the world reached 1.4 billion last year. That represented a 6% increase, and the organization forecast the number to grow by another 3 or 4% in 2019.

But in the first half of 2019, the number of international visitors coming to America has actually dropped nearly 1.7%. That's according to preliminary data from the Department of Commerce's National Travel and Tourism Office, which shows slightly more than 37 million foreign travelers came to the country between January and June.

According to a forecast from the U.S. Travel Association, an industry trade group, the outlook for 2019 is for visitor numbers to remain just about the same as last year. Even if that holds true and the country doesn't see a dip for the full year, the news is not good.

"It's generally going to be under-performing global travel," says David Huether, the group's senior vice president of research.

There's a grab bag of reasons for the downturn, observers say. The latest version of a monthly report from the U.S. Travel Association, out this week, warns that foreign visits to the country remain vulnerable.

"Ongoing global economic cooling, prolonged and expanding trade tensions, and uncertainty surrounding the Trump administration remain major risks to international traveler sentiment," the report says.

The value of the U.S. dollar also remains strong, making travel more expensive for visitors from other countries, Huether says.

Trade wars with China could cost the country 1.9 million inbound visitors and $11 billion in spending between 2018 and 2020, according to research from the consultancy Tourism Economics, part of Oxford Economics. Through July, travel from China is down 3.7% compared to last year, according to commerce department figures. That's on top of a drop last year, the report says.

"Someone should care about this as much as they care about U.S. auto manufacturing or agriculture," says Adam Sacks, president of Tourism Economics. "Given the size of the traveling class in China and how much that's grown and the strong desirability that the U.S. holds in Chinese travel intentions, we'd expect to see growth in the range of 10%. Instead, we saw a 5.7% decline."

China warned its citizens about traveling to the United States in June, naming gun violence, robberies and theft as risks. Citing two mass shootings over the same weekend in August, the governments of Uruguay and Venezuela, as well as Amnesty International, issued travel warnings of their own.

Huether said the U.S. Travel Association is considering ways to see if concerns about gun violence keep potential tourists away.

"It's easy to believe that incidents like these could have an effect on travel, but we can't at this point conclusively say based on the data that's available," he said in an August interview. "We are going to be exploring ways to see if we can measure that."

Furthermore, Sacks says there is a larger issue of public sentiment that should worry the nation. He believes some potential visitors might be staying away because they disagree with policies on immigration or the U.S. withdrawal from the Paris climate agreement. Sacks said he has heard anecdotally from clients about conventions and other travel groups that have canceled plans to visit on moral grounds.

"There's going to be pockets of the traveling public that, out of protest for unfavorable U.S. policies, are not traveling to the U.S.," Sacks says.