Last week, I completed a writing project on Japan’s experience with imperialism, just two hours before the deadline. Finished, I felt exhilarated. Free!

The writing itself, by contrast, had depressed me. I love my country; trying to explain the way Americans in the mid-1800s forced a weak nation to sign treaties that we knew to be “unfair,” left me sad when I wasn’t angry. I also love Japan; trying to understand why it turned imperialist, then warlike, in response to those Western pressures also left me sad. And angry.

Why? I asked again and again. What leads a nation, a good people, to abuse another? What caused the Japanese to keep seeking more territory in the early twentieth century, then to make those cursed decisions that led to Pearl Harbor . . . then to Hiroshima and Nagasaki?

I offered all of the standard answers in my manuscript. Pushed into empire-building by the Western threat, the Japanese couldn’t change their imperialist habit. The Great Depression caused Japan to turn from internationalism to a self-obsessed go-it-alone policy in the early 1930s. Militarists and nationalists took the initiative away from democrats and internationalists in the troubled Depression milieu.

All of those answers contain a great deal of truth. At the same time, I have become convinced that there was another, very theological, very human explanation. Simple as it sounds, Japan’s descent into aggression was fueled in fundamental ways by an inability to understand that all peoples are one.

When we see ourselves as separate, isolated, superior–anything less than connected to every other being–it is a short step to hurtful and dehumanizing behaviors. When we see other people (or peoples) as Other, when we cannot see that they are connnected to us, it is easy to treat them differently from the way we treat ourselves, or want to be treated.

When Westerners sent their gunboats to Japan in the 1850s, they regarded the East Asians as different: pagan, uncivilized, backward. They knew almost nothing about them; what knowledge they did have was often inaccurate. But in their hearts they knew the Japanese to be of another kind–which made it easy, even rational, to treat them unjustly.

When the Japanese moved into Korea and China in the 1900s, they did the same thing. They saw the Koreans and Chinese as different: uncivilized, primitive. They knew more about them than the Americans had known about Japan, but their conviction that continental Asians were Other made it easy to talk about bringing “civilization to the benighted” even while treating them as objects rather than as sisters and brothers.

The mystics and spiritual giants have had no more radical insight than their understanding that all beings are one. The Dao De Jing says of a sage: “The more he does for others, the more he has himself.” Of course: the sage is connected to others; something done for another is done for (and to) one’s self.

Thomas Merton said the same thing when he argued that we all are one; we only have a misapprehension that we are not.

If an Israeli does not understand that she is one with her Palestinian neighbor, how easy it is to treat that neighbor as if she did not exist, or to take away her right to live a fully human existence. If a Palestinian is blind to his oneness with the Jewish settler nearby, lobbing a bomb makes sense.

An American who regards a Taliban activist as Other (the label matters little: extremist, terrorist, fanatic) has little trouble justifying a heartless curse or a nasty attack on an Afghani village. Nor will the Al Qaeda suicide bomber think twice before killing the American Others who dominate her nightmares and day-visions.

Take away Merton’s understanding that we are one, and the decisions become easier. Ask myself, on the other hand, how my actions will affect me (because the Israeli, the Palestinian, and the Taliban activists are me) and the decisions become much more difficult. They also become more humane.

Japan’s prime minister Tojo Hideki reportedly told a reporter in 1948, as he awaited execution for war crimes, that nations think of themselves as fighting for “justice and self-preservation,” but actually war “stems from human greed”–from gaining an advantage for myself over the Other. When the reporter asked if he had thought that way while he was prime minister, he said no, he had realized it only after the war, while sitting in jail.