Terrorism, weapons of mass destruction, concern about Russia and strife in the Middle East are nothing new. Our grandparents and great-grandparents were all too familiar with them, starting 100 years ago this week.

It was on April 6, 1917, that the United States declared war on Germany.

Our entry into World War I is remembered by almost no one alive today. The last doughboy, West Virginia Frank Buckles, went over the top to his final reward a few years ago.

But America’s participation in the Great War began a new chapter in our history — one still being written.

We as a nation had hoped wide oceans, our military and economic strength and our determination could isolate us from conflicts we felt were none of our business. We were wrong then, yet have continued over and over again to indulge in that futile hope.

World War I did not make us a great power, but it did make our strength apparent to the rest of the world. We continue to struggle with that burden.

Much of the peril we face today is rooted in the period during which World War I was fought. Russian communism, leaders of which still control that country, seized the opportunity war presented. Partitioning of the Middle East by World War I’s victors created or aggravated enmities we struggle today to resolve.

War in the past had relied on weaponry of limited deadliness. World War I changed that, bringing true weapons of mass destruction on the scene. By the hundreds of thousands, men expecting to fight as their fathers and grandfathers had were mowed down by machine guns that may have killed more people than were claimed by atomic bombs a few decades later.

Mass killing made more terrible by new weapons such as aircraft, poison gas, tanks and long-range, heavy artillery shocked the world.

Terrorism was in the headlines, too, in the form of a practice Americans considered so abhorrent that it helped take us into the conflict: unrestricted submarine warfare.

Americans’ participation in World War I changed our nation fundamentally, in ways that affect us and the rest of the world still.

Once the conflict ended, the horror and magnitude of what humankind had done in four years made some hope it had been the war to end wars. They reasoned rational people would not allow such a thing to happen again.

Sadly, in the century since we began sending American troops “over there,” the only lesson we seem to have learned is this: The optimists were wrong.