States and the United Kingdom. Since the dues were payable based on weight, periodicals would be assessed much higher terminal dues than letters. The continuing fiscal imbalances required repeated changes to the system of terminal dues. In 1988 a per-item charge was included in terminal dues to drive up the cost of remailing, an old scourge that had returned. To resolve the problem with periodicals, the UPU adopted a "threshold" system in 1991 that set separate letter and periodical rates for countries which receive at least 150 tonnes of mail annually. The 1999 Postal Congress established "country-specific" terminal dues for industrialized countries, offering a lower rate to developing countries. Shifting balances and the United States In 2010, the United States was a net sender because it was mailing goods to other countries. That year, the United States Postal Service made a $275 million surplus on international mail. In addition, the UPU system was only available to state-run postal services. Low terminal dues gave the United States Postal Service an advantage over private postal services such as DHL and FedEx. To protect its profits on sending international mail, the United States voted with the developing countries to keep terminal dues low. They were opposed by the German Post and the Norwegian Post, which wanted to increase terminal dues. However, the low terminal dues backfired on the United States due to shifts in mail flows. With the growth of e-commerce, the United States began to import more goods through the mail. In 2015, the United States Postal Service made a net deficit on international mail for the first time. The deficits increased to $80 million in 2017. The UPU established a new remuneration system in 2016, a move that the United States Department of State said would "dramatically improv[e] USPS's cost coverage for the delivery of ... packets from China and other developing countries." However, the Chairman of the Postal Regulatory Commission disagreed. 2019 Extraordinary Congress With the outbreak of the China–United States trade war in 2018, the issue of terminal dues was pushed into the forefront. Americans complained that mailing a package from China to the United States cost less than mailing the same package within the United States. At the time, the UPU's Postal Development Indicator scale was used to classify countries into four groups from richest to poorest. The United States was a Group I country, while China was