World War I, which ended 100 years ago Sunday, was to be, according to President Woodrow Wilson, “the war to end all wars.” It actually turned out to be the war to start all wars — at least all modern wars. Among dubious “firsts” remaining as legacies of the so-called “Great War” are the flamethrower, the machine gun, the tank, the combat airplane, and gas masks for chemical warfare. Conservative estimates put the total number of deaths from World War I at just under 40 million — but the actual number? God only knows. We do know that the last Great War veteran died in 2012. We let the lessons of the Great War die with that veteran at the world’s collective peril.

So on this Veterans Day centennial, is it not fitting to reflect and ask, “What did those 40 million deaths buy?” That is, what did the price paid in such an unfathomable amount of blood, horror, and sorrow yield? Hindsight being what it is, we know this to be an unfair question in a certain sense. After all, World War II was just around the corner, with death tolls dwarfing those of the Great War. But can we not still look back and ask, “What, if anything, did we — more importantly, should we — learn?” The answers aren’t easy to come by, not because they aren’t apparent but because most of us have never really studied them. But don’t we want to know?

Perhaps not, as historian Allen Guelzo notes: For all its “greatness” the Great War has no monument on the National Mall. But as early 20th century U.S. poet and philosopher George Santayana aptly noted, “Those who cannot remember the past are condemned to repeat it.” But repeating World War I might very well be an extinction-level mistake.

World War I began July 28, 1914, and ended November 11, 1918, leaving in its wake three destroyed empires (Hapsburg, Ottoman, and Romanov), a new, highly volatile world order, and a shell-shocked global witness to the sheer destructive power made capable by emergent Industrial Revolution technologies and catastrophic miscalculations of men. The failure of world leaders to appreciate and grapple with the war’s aftermath also directly led to the rise of Hitler, Stalin, and another, even more horrific, world war. Many historians note that although the evidence was plain to see after the fact, very few saw the War coming at the time — and no one foresaw the severity and extent of the war’s devastation. Looking back now, a hundred years after the War’s end, a number of lessons are apparent that should never be forgotten.

What lessons? War should not be the first answer to every problem, it should be the last answer to an inescapable problem. Other instruments of national power — diplomacy, economic pressure or relief, and the like — should be used until they are exhausted. The so-called “experts” — to include military and political leaders — likely have no idea about the Pandora’s box of unintended consequences they are opening when they resort to force, only to find they can’t put the lid back on them, once released.

War is unpredictable by its very nature and, generally, the bigger the war the more unpredictable the outcome. The war envisioned by a nation’s leaders is never the war the nation will actually fight — hence the extreme gravity with which such decisions should be made. Technology moves at a pace that far outstrips man’s ability to understand and cope with its impacts — especially in war. Propaganda-fueled mass movements are much more likely to end in horrific tragedy than in the Pollyanna end-state envisioned by their proponents. The victors will always carve a new map. However, it is a fool’s errand to carve such a map without regard to prewar cultural, religious, and ethnic demographics, and it’s much more likely to sow the seeds of future conflict than to settle it.

Joining a war without a definite national security interest at stake is reckless and could put a nation’s people at needless risk of loss of life; not joining when a national security interest is at stake can yield even worse outcomes. Immediately after a war, declaring victory and going home is politically appealing, but failing to stabilize a war-ravaged, defeated nation is a formula for future war. Defeating an opponent is one thing; continuing to exact revenge on that opponent even after its defeat is another, with predictable results when the shoe is on the other foot.

These do not present an exhaustive list of the lessons of the Great War, but they do constitute some of the most important lessons.

An analysis of each lesson and its moral is a study unto itself, but practical constraints bar such a deep-dive here. The more important point is that we are indeed doomed to repeat these lessons if we cannot remember them, and the vast majority of America’s children will never come in contact with them in today’s politically driven school systems, whose curricula have been thoroughly infused with post-modern, neo-Marxist leftist ideologies. But as parents, we owe our children the duty to teach them these lessons regardless of whether they learn them in school. That means getting up to speed on them ourselves, if need be. A good starting point is Michael Neiberg’s excellent book, Dance of the Furies: Europe and the Outbreak of World War I. The world cannot afford to repeat the errors of the Great War. Committing its lessons to memory is the best preventative to this malady — it’s also one of the best ways to honor the 40 million who made the ultimate sacrifice so we have those lessons.