More than 20,000 protesters are expected to cram into a 1.4 mile-long court-approved protest route near Democratic National Convention in Chicago next week, creating a potential standoff between demonstrators and a police department with a history of excessive force.

The 264 protest groups that have said will participate are primarily focused on Palestinian rights, ending the war in Gaza and reducing U.S. aid to Israel. Others represent a patchwork of left-leaning causes: climate activists,…