Trade wars and political unrest contributed to a fall in global sales across the art market in 2019, according to a new report.

Following two years of growth, global sales of art and antiques fell to 5 percent year-on-year to $64.1 billion last year, according to the Art Market 2020 report.

The fourth edition of The Art Basel and UBS Global Art Market Report revealed that the United States, the United Kingdom and China remain the three largest art markets by value, accounting for 82 percent of global sales.

"The challenges of operating in an unpredictable global macro environment have had an impact on many businesses in the art market," said Clare McAndrew, report author and Arts Economics founder. "Uncertainties have fed into the selling and buying plans of vendors and collectors."

The US was the largest art market with 44 percent of sales, or an estimated $28.3 billion.

The UK market accounted for 20 percent of global sales, falling 9 percent from 2018 following Brexit uncertainty, and China remained the third-largest market, representing an 18 percent share, with sales estimated at $11.7 billion.

"International cross-border flows of art currently also face a range of opposing forces, from increasing trade regulations and tariffs, to the drive to purchase more locally to reduce the art market's impact on the environment," McAndrew said.

France was the only market to buck the declining trend, with sales rising 7 percent in value to $4.2 billion, increasing France's global share from 6 percent to 7 percent.

After two years of consecutive growth, public auction sales fell 17 percent in 2019 to $24.2 billion. Sales in all the leading markets were down. In China, auction sales were down 16 percent to $7.1 billion, "driven by lower values in older fine art and decorative art and antiques sectors."

"Slowing economic growth and the prolonged and volatile trade wars with the US were reported as having negatively influenced both buyers' and vendors' participation in the market, as well as new buyers being deterred by the negative recent performance of the auction market," according to the report.

Despite the decline in public auction sales, private sales increased, including sales of more than $1.8 billion at Christie's and Sotheby's.

In the gallery and dealer sector, sales grew just more than 2 percent year-on-year, reaching $36.8 billion.

A survey on 1,300 high net worth individuals in seven markets found that millennial collectors, those aged 23 to 38, were the most active buyers and spent the most.

On average, millennials spent $3 million over two years, that's more than six times the spending of Boomers, those aged 55 to 73.