The following essay is reprinted with permission from The Conversation, an online publication covering the latest research.

The 2016 American presidential campaign has renewed concerns about the specter of violence in American electoral politics. The campaign has been marked by tense—and occasionally violent—altercations between supporters and critics of Republican nominee Donald Trump.

Trump encouraged his supporters to “knock the crap” out of protesters, and even suggested he would pay the legal fees of followers who assaulted his critics.

By refusing to commit to accepting the results of the election, he has confirmed the doubts among his supporters about the integrity of American elections. Thereby, he has increased the risk of possibly violent resistance by hard-core Trumpists.

It would be comforting to conclude that the menace of violence surrounding the 2016 presidential election is unique. But my research on the history of voting rights in the United States suggests that this is far from the case. Indeed, the threat and execution of violence around elections has a long, sad history in American politics.

Somewhat like the 2016 election—which has revolved around issues of race and immigration—efforts by disadvantaged (and often nonwhite) citizens to secure greater political influence have been met with violent repression by those already enjoying power (usually more affluent whites) throughout American history.

History of violence

Violent conflict surrounding elections goes all the way back to the beginning of American history. The Founding Era—often portrayed as a period dominated by outstanding, level-headed statesmen who set the United States on a course toward inevitable greatness—was actually a chaotic period.

Political violence was a constant threat in that period. And, occasionally, a reality.

In 1804, Aaron Burr, vice president and an aspirant for higher office, killed Alexander Hamilton, George Washington’s former secretary of the treasury, in a duel. Doubting Burr’s judgment and patriotism, Hamilton had worked to deny Burr the governorship of New York. Burr was outraged over Hamilton’s efforts to deny him the political success he craved.

The period between the 1820s and the onset of the Civil War was marked by a substantial increase in ethnic and religious diversity. This period was also notable for an increase in violent conflict surrounding politics and elections.

In a precursor of today’s politics, these clashes stemmed from heightened anxieties among native white Protestants about the consequences of Irish and German Catholic immigration for American identity and social harmony.

Of particular note was the rise of the virulently nativist, anti-Catholic “American Party” (better known as the “Know-Nothing” Party) in the 1850s. For some Know-Nothings, violence against recent immigrants was an acceptable means to preserve the rights of native whites.

The Know-Nothings were hardly a fringe movement: By 1854, they had elected 52 of the then 234 members of Congress, as well as the mayors of several major cities. The rise of the Know-Nothings triggered serious conflicts between native white Protestants and those who had recently immigrated.

In a particularly horrifying 1855 event known as “Bloody Monday,” 22 people—mostly recent German and Irish immigrants—were killed, and many more were injured, in an Election Day riot in Louisville, Kentucky.

In a disturbing precedent given Trump’s request that his supporters monitor polls in “certain locations,” an immediate precursor of the riot was an effort by armed Know-Nothing supporters to prevent eligible immigrant voters from casting ballots.

The deadliest conflict

It also bears remembering that the Civil War was sparked by the refusal by southern states to accept the results of the 1860 election.

That unusual contest, which had featured four major presidential candidates, had been won by Republican standard-bearer Abraham Lincoln despite the fact that he secured only 39.9 percent of the vote.

Although Lincoln did not support the immediate emancipation of African-American slaves, southern leaders believed he intended to destroy the southern slave system. They sought to exit the Union in order to prevent that from happening.

When Lincoln refused to accept southern secession, the result was the Civil War—still the nation’s deadliest conflict in terms of total casualties.

Racialized election violence

But violence directly linked to elections arguably reached a fever pitch in the decades following the North’s victory in the Civil War. The national Republican Party’s attempts to enfranchise African-Americans and strengthen Republican Party organizations in southern states were contested strenuously—and often violently—by southern whites.

In the 1870s, 1880s and 1890s, armed groups of newly enfranchised African-Americans and their white Republican supporters repeatedly squared off against white supremacist paramilitary organizations in states throughout the South.

In one of the worst single episodes of violence—the Colfax Massacre of 1873—a group of white vigilantes killed somewhere between 62 and 150 African-American men. African-American Republicans had occupied the Grant Parish, Louisiana courthouse in order to preserve the results of the 1872 gubernatorial election, which had elevated a Republican to the governorship. Three whites were also slain in the battle, which had featured the use of trenches and cannon.

A long history

The threat—and repeated execution—of violence remained important features of efforts by white supremacists to suppress African-American (and Latino) registration and voting all the way up until enactment of the Voting Rights Act of 1965, which strengthened federal voting rights protections and authorized federal monitoring of election rules in states with records of racial discrimination in voting.

Indeed, the immediate impetus for enactment of the Voting Rights Act was widespread public outrage following the nationwide broadcast of images of the brutal police suppression of a peaceful voting rights march in Selma, Alabama.

And the subsequent expansion of the Voting Rights Act to protect the rights of non-English-speaking Americans was shaped in no small part by reports of the violent intimidation of prospective Latino voters, especially in southwestern states.

Just a few years after enactment of the Voting Rights Act, the 1968 Democratic National Convention was famously marred by the violent suppression of anti-war demonstrators by the Chicago police. Demonstrators explicitly portrayed American involvement in Vietnam as the continuation of American imperialism and suppression of nonwhite peoples. The clash represented another example of racialized violence surrounding elections.

As a general matter, elections in more recent decades have been characterized by greater civility. However, the long history of violence in American elections should caution citizens against undue optimism about the continuation of this recent favorable trend.

Trump’s incitement of violence and denigration of the integrity of American elections do, in fact, risk the resumption of ugly historic patterns.

This article was originally published on The Conversation. Read the original article.