President Woodrow Wilson called it “the most terrible and disastrous of all wars.” Winston Churchill described it as the moment when “all the horrors of all the ages were brought together.” H.G. Wells labeled it “the war that will end war.” Sadly, none of them were correct. A more terrible, more disastrous war followed a generation later; humanity mixed old hatreds and new isms to produce unspeakable horrors after the Great War; and the war to end all wars spawned a second global war, which spawned the Cold War, which spawned uncounted hot wars and proxy wars that further deformed humanity. Yet here, in the middle of the centennial anniversary period of World War I, we still find ourselves in the shadows of the Great War—and still have much to learn from it.

A first lesson is that treaties, international law and the like are not enough to keep the peace or protect U.S. interests. Wilson realized this, albeit far too slowly. It pays to recall that when German U-boats began attacking merchant ships, Wilson vowed to hold the Kaiser to “strict accountability.” Yet after Americans were killed aboard the Falaba, Lusitania and Arabic, he responded by writing letters.

President Theodore Roosevelt, who became something of a one-man shadow government during the war, put it well in 1914: “In time of crises, peace treaties are worthless.” He hammered that point repeatedly during the war, pointing out the “utter worthlessness of treaties” and how they “offer not even the smallest protection against such disasters.”

Importantly, these words come from a man who believed in diplomacy, a man who negotiated important treaties that staved off and ended wars in Europe, Africa and the Pacific, a man who earned a Nobel Peace Prize for his diplomatic efforts. Yet his years of experience taught him that “diplomacy is utterly useless where there is no force behind it.”

A century later, this truth remains unchanged because man’s nature remains unchanged: Bad guys do bad things. A piece of paper, a presidential address, a UN resolution, a portfolio of sanctions seldom correct or prevent bad behavior. None of these stopped Putin from annexing Crimea; or China from building illegal islands in international waters; or North Korea from firing missiles or testing nukes; or jihadists from mutilating Iraq, or maiming Manhattan, or laying siege to Paris and London; or Iran from lurching toward the nuclear club; or Assad from bludgeoning his people—or reopening the Pandora’s Box of chemical warfare.

Germany was the first to use poison gas during the Great War—a chlorine-gas attack in Belgium in 1915. It was effective, and the Allies followed suit. By the end of the war, chemical weapons had killed 91,000. Postwar treaties tried to close Pandora’s Box, but chemical weapons have been used in at least 11 conflicts since 1919, most recently by Assad and ISIS. As before, as always, international agreements to disarm the guilty and promises made by the guilty have failed to stopthe guilty from backsliding.

The reason: Treaties and other international agreements are only as good as the character of the governments that sign them. Consider the Kellogg-Briand Pact, an ambitious treaty to outlaw war conceived by the U.S. and France in a heady and hopeful flurry of diplomatic activity after the Great War. Less than 12 years after it was signed, Japan, Germany and Italy—all original signatories—would attack virtually all of the other original signatories.

While words alone often fail to keep the peace, diplomacy backed by the credible threat of force can be highly effective. It was during a summit, the very height of diplomacy, after Nikita Khrushchev boasted about the Red Army’s overwhelming conventional edge in Germany, that President Dwight Eisenhower coolly responded, “If you attack us in Germany, there will be nothing conventional about our response.” Khrushchev got the message. Likewise, President John Kennedy reinforced U.S. diplomacy during the Cuban Missile Crisis by lofting 90 nuclear-armed B-52s into round-the-clock orbits over the Atlantic and dispatching 60 warships to the waters around Cuba. Again, Khrushchev got the message.

More recently, President Ronald Reagan’s military buildup led to the first treaty that eliminated an entire class of nuclear weapons, then to reductions of strategic and conventional weapons, then to victory in the Cold War. And it was the very real threat of force that convinced Libya’s Muammar Kaddafi to hand over his vast WMD program in 2003, after he became convincedhe would meet the same fate as Saddam Hussein.

That leads us to a second lesson from the Great War: Military preparedness can go a long way to keeping the peace, while unpreparedness invites danger.

America was ill-prepared in 1914, as TR detailed. “Our navy is lamentably short in many different material directions. There is actually but one torpedo for each torpedo tube,” he wrote. “For nearly two years, there has been no fleet maneuvering.” Hence, the Kaiser neither feared nor respected the U.S.

“The United States has never once suffered harm because of preparation for war,” TR explained. “But we have suffered incalculable harm, again and again, from a foolish failure to prepare for war.” Being prepared for war, TR understood, is cheaper than waging war. In the eight years before entering World War I, the United States devoted an average of 0.7 percent of GDP to national defense. During the war, U.S. defense spending spiked to 16.1 percent of GDP.

America returned to its old ways after World War I. In the 1930s, the United States spent an average of 1.1 percent of GDP on defense annually—then came Pearl Harbor.

Applying the lessons of deterrence, Americans spent an average of 7 percent of GDP on defense during the Cold War to keep the Red Army at bay. It worked.

Yet it seems Washington has forgotten those hard-learned lessons in recent years, as the bipartisan gamble known as sequestration has guillotined America’s deterrent military strength. The U.S. defense budget has shrunk from 4.6 percent of GDP in 2009, to around 3 percent of GDP today. All the while, Beijing increased military spending 55.7 percent between 2011 and 2015. Last year, Beijing increased military spending another 7 percent. Moscow increased military spending 108 percent between 2004 and 2013; Moscow’s 2015 military outlays were 26 percent larger than in 2014.

It is far wiser to make the relatively small investments necessary to deter war than to expend enormous amounts of wealth and human life to wage war. For even when it is necessary, war is terrible and terrifying, wasteful and awful. God’s crowning creation is not made for war.

The Great War was romanticized when the guns thundered to life in August 1914, but those who survived the trenches realized it was more apocalyptic than romantic: Like Revelation’s Four Horsemen, it brought conflict (28 nations were engaged), famine (Belgium starved; Germany survived on turnips; Austria’s cities went hungry), death (10 million soldiers and 6 million civilians died) and pestilence (the 1918-19 influenza pandemic claimed 50 million). 

Perhaps this explains why Wilson described leading America into the Great War as “a fearful thing.”