So if you read the headlines, it kind of seems like the world is a terrible place,

full of violence, despair, and war.

But it turns out war 's actually declining.

We live in the most peaceful time in human history.

There's lots of reasons why, but here's three of the biggest ones.

First, the spread of democracy around the world.

International relations scholars have found consistently that democracies don't fight wars with each other.

Now why is that true?

There might be plenty of reasons

but one big one is that people who live in democracies think it's wrong to start wars with other democracies.

They're legitimate governments.

It's wrong to attack them.

But there's a flip side to this.

Democracies do often fight wars with autocracies.

Luckily, most of the world 's countries are democracies now,

so the democratic peace is probably making the world a much more peaceful place.

Second big reason why war is declining is nuclear deterrence.

Nuclear weapons, obviously big and scary.

However, nuclear deterrence may have prevented a devastating war between the United States and the Soviet Union.

Everyone recognized that they would lose.

Statistical evidence suggests that that is true,

that is that most countries are too scared of the consequences of nuclear war to fight one.

There's a dark side,

and not just the risk of global annihilation from an accident.

If a country gets nuclear weapons, they feel rather safer in being aggressive in little ways,

you know, small conflicts or bullying around their non - nuclear neighbors.

This weird paradox, that nuclear weapons make the world more violent and more peaceful at the same time, is called the Stability-Instability Paradox.

The third reason that war 's declined has been the spread of the idea of national sovereignty.

This idea is hundreds of years old,

the idea that you shouldn't interfere inside the borders of another state.

But people didn't take the idea too seriously,

because stealing new land used to be a major cause of war.

Think American European colonialism or World War II.

But after World War II, nations pledged to stop.

Since 1976 there has n't been a single successful war of conquest,

except for maybe Russia in Crimea, really recently.

Again though, sovereignty has a flip side.

Sometimes governments go to war against their own people,

and poor, weak governments often collapse into civil war.

Sovereignty makes it hard for the international community to intervene to stop either of those kinds of wars.

But on the whole, when you see those terrible headlines,

remember the world 's way better off than it ever has been.

There's less war and less violence than almost any other time in human history.

That's something worth celebrating.