More guns were sold in December than almost any other month in nearly two decades, continuing a pattern of spikes in sales after terrorist attacks and calls for stricter gun-buying laws, according to federal data released on Monday.

The heaviest sales last month, driven primarily by handgun sales, followed a call from President Obama to make it harder to buy assault weapons after the terrorist attack in San Bernardino, Calif.

Fear of gun-buying restrictions has been the main driver of spikes in gun sales, far surpassing the effects of mass shootings and terrorist attacks alone, according to an analysis of federal background check data by The New York Times.

During the previous record month, December 2012, President Obama called for new buying restrictions after the mass shooting at Sandy Hook Elementary School.