The American Civil War was the most deadly and arguably the most important event in the nation's history. Sectional tensions enshrined in the Constitution erupted into a brutal war that cost over 600,000 lives and cleaved a nation in two. 

It was a war that would come to define America—that would answer the "slavery question" once and for all. Were we a nation committed to the ideas of the Declaration of Independence that "all men are created equal" or were we really two separate nations that should just go their separate ways and cut their losses?

When the South peaced out and created its own country, the Confederate States of America, it didn't take long for Lincoln to protest. His idea was to try and settle this without any bloodshed.

Oh, what a cute thought, Abe.

Once the first shots were fired and war was official, people thought it was going to be a quick and easy war, over in a matter of weeks.

Oh, what a cute thought, Americans.

After the bloodshed at the First Battle of Bull Run, Americans realized they were in for something else entirely. In fact, they were in for the bloodiest war in history to date. Things were going to get a whole lot worse before they got better. The war touched every aspect of American life, for both soldiers and civilians, and its effects are still being seen today.

Slavery was a root cause of the conflict, and while the 13th Amendment ended the practice at war's end, race relations continued to dominate American politics and society well into the future. The war also increased American economic power until it rivaled, and then surpassed, that of all other countries. 

But it wasn't—and arguably, still isn't—a pretty journey.

The Civil War is one of the most—if not the most—important event in the history of the United States. 

The American Revolution? Sure, we got some freedom. The creation of the U.S.Constitution? Yeah, that's key. The last episode of The Sopranos? Up there. 

But few things in American history changed this country like the Civil War. We're not being too bold when we say that everything in American history leading up to 1860 was a cause of the Civil War, and everything that's happened since was caused by the Civil War.

Every part of American society was fundamentally changed, from the role of the federal government to the status of African Americans to the art, music, and culture of a nation. Over 600,000 Americans died in the conflict, more than in all other American wars combined except for the Vietnam War. And all of them died on American soil. 

Brothers fought brothers. Fathers shot sons. What began as a small-scale bombardment of an average fort in Charleston, South Carolina, grew and grew, ultimately killing more than 2% of the population and reforming the United States in ways big and small.

But the Civil War and all of its causes and effects can't be absorbed easily. After all, it was a huge conflict, brought about by deep-seated forces and fought across the entirety of the American continent, from Gettysburg to Vicksburg, and Savannah to San Francisco. 

So, how do you get your mind around an event of this magnitude? How do you try to understand what the Civil War was all about?

Well, you start here, and as you read, you think big. Imagine 150,000 men attacking each other in a place like Maryland. Consider the noise, the fear, the terror, and the death. Imagine yourself listening to the cries of the wounded in dirty hospitals, doctors operating without anesthesia, and more wounded men flooding in all the time.

Think about the joy of newly emancipated slaves, who had labored their entire lives under the watchful eyes and often violent hands of white Southern planters, finally free to determine their own destinies. 

And think about the very meaning of the country. Is the United States one nation, indivisible? Or is the United States a collection of linked but autonomous states? 

The Civil War changed even the language we use to describe the nation. Before the Civil War, Americans used the phrase, "The United States are..." but after the war, that phrase became, as it is today, "The United States is..."

A cataclysmic conflagration like the Civil War profoundly changed the way in which Americans envisioned their own nation, seeing it no longer as a grouping of autonomous states but as one nation, indivisible. For better or for worse, the Civil War altered the fabric of the idea that is the United States.

And that's definitely food for thought.