World War I is seared into our historical memory as the first total war. Fought between 1914 and 1918, the event inspired books, films and articles that grappled with the question of how humanity could allow such destruction and loss of life to take place. And yet World War I was not the first, nor the deadliest, mass war in history. Four hundred years ago, another armed conflict brought even greater death and destruction upon the European continent. But its anniversary came and went without fanfare.

May 23 was the 400th anniversary of the outbreak of the Thirty Years’ War, a conflict rivaled only by World War II in loss of life and property damage in Europe. By the time the Thirty Years’ War ended in July 1648, it had laid waste to an area that today constitutes most of Germany, Poland and the Czech Republic, while killing nearly 40 percent of the population of Central Europe.

So why have we forgotten such a crucial event in history?

The Thirty Years’ War was a complex conflict, one unfamiliar to modern sensibilities shaped by conflicts of good vs. evil and battles between clearly delineated nation-states for power, land or influence. And yet, while a war that happened in the Holy Roman Empire over four centuries ago seems distant, it may hold the key to understanding the very real challenges of war in places like Syria today. To understand these conflicts, we must shatter our conventional notion of war — which we can do by understanding complex conflicts like the Thirty Years’ War.

The Thirty Years’ War broke out in 1618 after an incident known as the Defenestration of Prague, in which Protestant representatives from the kingdom of Bohemia (the western part of the present-day Czech Republic) threw three government officials representing the Catholic Habsburg dynasty out a window of Prague Castle. Similar to the shots in Sarajevo that started World War I nearly 300 years later, the Defenestration of Prague was an event of regional significance that caused a ripple effect across the international networks of its time, igniting the powder keg that was the European continent a century after the Protestant Reformation broke Christendom apart.

During its three decades of hostilities, the Thirty Years’ War was never a clear-cut conflict. In fact, the Thirty Years’ War was so unwieldy that historians debate whether it can even be considered a coherent war.

To make sense of it, the war has been divided into four phases. The first phase, known as the Bohemian Phase, was a regional armed conflict centered on the religious tensions between the Catholics and Protestants of Bohemia and the city of Prague. The second phase is called the Danish Phase, because the Danish King Christian IV interfered to protect his position in Central Europe.

The third phase is when the war developed into an international conflict when Sweden intervened on behalf of its Lutheran brothers and sisters. Of course, the Swedes also wanted to protect their position in the Baltic. To achieve this goal, they entered into an alliance with France, which in effect turned the Swedish war effort into a French proxy war against the Habsburg dynasty. The fourth and final phase of the war began when France officially entered the conflict and declared war on its archenemy, Spain. Only then did the Thirty Year’s War become a global war that spilled into trade relations in the combatants’ respective colonies.

In short, it is difficult to pinpoint who was fighting whom. The war began as a constitutional and religious conflict between Catholics and Protestants in Eastern Europe but ended in a showdown between the two Catholic superpowers of the time, France and Spain. The alliances were constantly changing, because they had more to do with dynastic politics and supporting the enemy of one’s enemy than with fighting for a cause. And neither side could be labeled as good or bad. Catholics and Protestants alike were guilty of war atrocities, as likely to be perpetrated against their own people as against their enemy.

In addition to this chaotic alignment and lack of a clear morally righteous side, the war also seems distant to modern eyes because it took place within the borders of the Holy Roman Empire, a geopolitical entity that has ceased to exist. Steeped in the mind-frame of the nation-state, we struggle to grasp 17th-century Central Europe in general, and the Holy Roman Empire in particular. Even historians of the early-modern period struggle to explain what the Holy Roman Empire actually was and how it functioned, because, as Voltaire famously put it, the Holy Roman Empire was neither Holy, nor Roman, nor an Empire.

The Thirty Years’ War came to an end in July 1648 with the signing of the Peace of Westphalia. But the end of the war was as inconclusive as the beginning. Hostilities ceased because the warring factions had run out of resources and manpower, not necessarily because the issues they were fighting over had been resolved. Moreover, the Peace of Westphalia itself was not one single peace treaty, but two, one signed in the German city of Osnabruck, and one in the neighboring city of Münster. And these treaties didn’t even completely end the fighting — they only concluded the war in the Holy Roman Empire. France and Spain continued warring for another 11 years.

The obscurity of the Thirty Years’ War in our historical consciousness serves as an example of how we search for linear, familiar narratives in the past as well as in our own time. When that narrative can’t be found, we move on to things we can better, and more easily, mold to fit our understanding of the world.

But this is exactly why we need to understand the Thirty Years’ War.

The public dismissal of complicated conflicts reveals an unwillingness to think outside the war narratives that emerged mainly during the 20th century. These narratives tend to distort our view of armed conflicts. Like the Thirty Years’ War, the civil war in Syria defies categorization. The civil war in the Democratic Republic of Congo takes place in a region we have difficulties relating to. The displacement of the Rohingya by the government of Myanmar upsets our preconceived ideas of who represents the good forces in the world and who represents the bad. All are occurring in far-flung parts of the world, making it even harder for Americans to comprehend what is happening, why it matters and which side we should be on (if any).

Only by understanding the more complicated and nuanced reasons violence breaks out and how wars are fought can we move beyond the simplistic narratives and perhaps expand our thinking on current conflicts. Placed within this context, the Thirty Years’ War becomes a conflict that, because of its complexity, we have chosen to forget, and which it is important that we re-remember.