Protests spread over police shootings. Police promised reforms. Every year, they still shoot and kill nearly 1,000 people.

Protests against the use of deadly force by police swept across the country in 2015.

Demonstrators marched in Chicago, turned chaotic in Baltimore, and occupied the area outside a Minneapolis police station for weeks. Protesters repeatedly took to the streets of Ferguson, Mo., where a white police officer had killed a black teenager the previous year and fueled anew a national debate about the use of force and how police treat minorities.

That year, The Washington Post began tallying how many people were shot and killed by police. By the...