It’s increasingly hard to tell these days where terrorism ends and warfare begins, to distinguish killing committed in the name of a cause from outright murder. Previous generations also struggled with it. Consider an incident from 156 years ago at an obscure Missouri waterway.

The Civil War is remembered as the time when blue fought gray. Yet it also contained a murky war within a war whose participants didn’t wear uniforms or carry flags.

Nowhere was that carnage worse than in Missouri. A border state that permitted slavery, its people were bound by cultural ties to the South and economic bonds to the North. Here the conflict was literally brother against brother, with entire families often divided.

Southern sympathizers living in northern Missouri were cut off from Confederates in the south. Some became guerrillas, small independent bands that struck targets of opportunity. Sometimes that target was military, sometimes it was civilian. In one bloody instance, it was both.

The new Hannibal and St. Joseph Railroad was strategically important in 1861. Stretching from the Mississippi River to the Kansas line, it was as far west as America’s rails went. It was so important, Ulysses S. Grant’s first Civil War command was guarding it.

The Hannibal and St. Joe (as locals called it) was the region’s premier transportation service. In 1860, it had carried the very first letter delivered from St. Joseph by the Pony Express. In 1861, it was carrying troops and military supplies for the Union. And that caught the guerrillas' attention.

On the moonless night of Sept. 3, they burned the 160-foot long wooden railroad bridge over the Platte River a few miles outside St. Joseph. They torched the lower beams but left the top intact. Then they waited.

Shortly after 11 p.m., a westbound train chugged into view. The locomotive rolled onto the bridge. With its lower structure charred, there was nothing to support the weight. The bridge collapsed and the engine plunged 30 feet into the river, spewing a geyser of scalding steam.

The baggage car, mail car, a few freight cars, and two passenger cars followed, all landing on top of one another like a crumpled accordion.

People screamed. The river boiled. Survivors staggered through the darkness to a sandbar and collapsed.

About midnight, Abe Hager, the train’s baggage master, climbed up the riverbank, found a railroad handcar, and rushed to St. Joseph for help. He rounded up of dozens of volunteers (including every doctor in the city) and medical supplies; a train sped them to the scene.

In all, around 20 people were killed. As many as 100 others were hurt, some maimed for life. The dead included at least one soldier, a Lt. Shaw, from a group of Union troops heading to Fort Leavenworth, Kan. Another fatality was Barclay Coppock, who had participated in John Brown’s infamous raid on Harper’s Ferry in 1859. Some guerrillas said they had hoped the pro-Union former Missouri governor and St. Joseph resident Robert Marcellus Stewart would be aboard. (He wasn’t.)

People tended to view the attack from the perspective of the side they supported. Sterling Price, commander of the state’s pro-Confederate forces, wrote to his federal counterpart saying that since soldiers were among the train’s passengers that qualified the attack as sabotage; thus participants who were captured should be treated as prisoners of war. Nonsense, Henry Halleck replied, the attackers were “spies, marauders, robbers ... in the garb of peaceful civilians” and would be hanged if caught.

In 2015, when an artist proposed a Civil War-themed mural for downtown St. Joseph that included the overturned train, city officials scrubbed it. The topic was still too hot to handle.

In fact, people couldn’t even agree on what to call the incident. Was it terrorism, warfare, or just plain murder? Defining it was just as hard then as it is now.

So folks settled on that saddest of words: The Platte River Railroad Bridge Tragedy. Which sums it up perfectly.

J. Mark Powell (@JMarkPowell) is a contributor to the Washington Examiner's Beltway Confidential blog. He is a former broadcast journalist and government communicator. His weekly offbeat look at our forgotten past, "Holy Cow! History," can be read at jmarkpowell.com.

If you would like to write an op-ed for the Washington Examiner, please read our guidelines on submissions here.