Mexico and the United States have reached a one-month agreement to stave off tariffs and a trade war, the threat of which sent global markets tumbling early Monday. The tariffs on Mexico were set to go into effect Tuesday.

Worries about President Trump’s tariffs are hurting U.S. stocks as financial markets worldwide drop on concerns about a potential trade war.

Uncertainty surrounds the trade war touched off by Trump’s tariffs. But some of the basics are taking shape.