Extremist groups thrived in the United States last year as the divisive rhetoric of national political leaders fueled America’s anxieties over the country’s shifting demographics, according to a report by the Southern Poverty Law Center.

The center found that the number of hate groups organized against racial, religious, sexual or other characteristics rose to 892 in 2015, up from 784 a year earlier.

The 14 percent increase came after three years of declines in extremist groups. Mark Potok, the author of the report, portrayed the shift as a product of white Americans’ heightened fears over their shrinking majority during a presidential election.

“I have been writing these year-in-hate and extremism essays for 20 years now and only very rarely, if at all, have we seen a year like last year,” Mr. Potok said.