Prime Minister Justin Trudeau of Canada warned that the Trump administration’s tariffs were leading to a trade war. Mexico’s leader vowed to impose countermeasures on Sunday.

Tariffs of 25% on Canada and Mexico that took effect overnight hit stocks today in a broad-based selloff following a steep drop Monday.

Tariffs on America’s three largest trading partners and retaliation by the countries are thrusting the U.S. economy and businesses into uncharted waters.