One year after Donald Trump’s upset election victory, it’s not unusual to hear people wonder out loud if the United States is really one country anymore. Last month, the Republican senator from Arizona, Jeff Flake, gave a speech on the Senate floor about the “state of our disunion.”

Recent polls have confirmed that Americans are feeling bitterly split. A Gallup pollconducted just after the 2016 presidential election found 77 percent of Americans see the country as “greatly divided when it comes to the most important values,” up from 66 percent in 2012. A Washington Post-University of Maryland poll, conducted nine months into Trump’s presidency, found that seven in 10 Americans think the nation’s political divisions are as bad as during the Vietnam War.

Some historians are also raising the alarm over division in the country. They say the rise of social media, combined with the decline of the central institutions that once defined the borders of political debate, have created a potentially dangerous moment in our public discourse. Today, even disasters seem to pull us apart more than bring us together. In the wake of mass shootings in Sutherland Springs, Texas, and Las Vegas and the devastation Hurricane Maria caused in Puerto Rico, social media was full of partisan debate over how to think about the events.