Tensions between Iran and Western countries have risen since the U.S. pulled out of the 2015 nuclear deal in 2018. The pact was intended to prevent Iran from developing nuclear weapons in exchange for relief from economic sanctions, but President Trump said it wasn’t tough enough. In May 2019, the U.S. imposed additional sanctions on Iran to try to force its government to restart negotiations. One result has been Iran’s seizure of oil tankers in the Strait of Hormuz, a choke point through which much of the world’s oil supply travels every day.