The mass demonstrations occurred on a day that historically has been the province of a variety of causes. May 1 is “Loyalty Day” in the United States, first proclaimed during the administration of President Dwight D. Eisenhower in the 1950s at the peak of “Red Scare” and Cold War era.

A massive crowd gathered at City Hall in Philadelphia Thursday for a May Day rally and to see Vermont Sen. Bernie Sanders speak. The "For Workers, Not Billionaires" rally on the north side of City Hall drew a large crowd and shut down streets in the area.

Thursday’s rally and march comes amid economic uncertainty created by Trump’s on-again, off-again approach to tariffs — taxes on imported goods — which