(CNN) In the spring of 1995, Gen. Rupert Smith, commander of the U.N. Protection Force in Bosnia, began warning that the Bosnian Serbs would soon try to take back zones that had been declared "safe" by the United Nations.
Not many took him seriously.
But slowly the assaults built. And on July 11, 1995, a massacre in Srebrenica would live in infamy. After years of indifference, the world could turn its head no more.
It was the worst atrocity on European soil since World War II, and the numbers are staggering to this day.
More than 7,000 men and boys were slaughtered simply for being Muslim -- part of the approximately 100,000 who would be killed during the war, the majority of them Muslim.
Just before the slaughter, Ratko Mladic, the Bosnian Serb military leader, was seen laughing with his soldiers, handing out candy, telling civilians not to worry. It is one of the most chilling pieces of video I've ever seen in my life.
It took the slaughter of thousands and thousands of people -- a genocide in the heart of Europe -- to get the American and European governments to be serious about putting an ultimatum to Slobodan Milosevic, the Serbian leader who used the Bosnian Serbs as his lethal instruments.
An enormous mortar attack on a Sarajevo market a month later was the final trigger. NATO bombed Serbian positions for two weeks. The Serbian forces were unmasked as brutal, but in the end became paper tigers -- they quickly surrendered. The Clinton administration tasked the late diplomat Richard Holbrooke with bringing the warring parties to Dayton, Ohio, and negotiate a peace that's held to this day.
For me, the war and what I witnessed changed everything. I saw the very best and worst of humanity.
The worst was the Bosnian Serbs, armed and backed by Milosevic, slaughtering civilians -- that meant women, little kids, old men.
Let's not forget that this was a deliberate slaughter of civilians -- not a war between two armies. The goal of the Bosnian Serbs was to terrorize and kill and ethnically cleanse these civilians from territory that they wanted to carve out as an ethnically pure statelet for themselves. They even had dreams of joining a greater Serbia.
It was a completely unlevel playing field, right down to the fact that they were perched on the mountains surrounding Sarajevo, shelling and sniping the mostly Muslim residents of Sarajevo, Srebrenica and other besieged cities that nestled in the valleys below. Nothing was off-limits: bread lines, water points, hospitals, schools; even road crossings made you a target.
It was hard to recall that only a decade earlier, the ethnically mixed, sophisticated and liberal city of Sarajevo had been the venue for the 1984 Winter Olympics.
Covering the war, it was hard to imagine the stadium where the British pair Jayne Torvill and Christopher Dean ice-skated into the history books -- because now it was an overflowing graveyard. It was hard to summon the music, "Bolero," that brought them a gold medal when all we could hear now was the pound of mortar fire and the whiz-ping of the snipers' bullets.
But war also brings out the best in people.
It brought out the best in those who resisted and those were survived, who clung to the belief that once this hell ended they could go back to living together again in their beloved multiethnic city, who despite the depravity of this war, their abandonment by the world, still kept their dignity, their humanity and their hope.
It was a privilege and a lesson for eternity to witness this heroic struggle and tell this story to the world.
As a young reporter, Bosnia is where I found my voice. As a person who had been taught the values of freedom, democracy, human rights, religious and ethnic tolerance -- to see all that under mortal threat in Bosnia -- Sarajevo, Srebrenica and all the other villages, towns and cities -- was formative. I resolved to do what I could to fight it -- through my words, our pictures and our huge and powerful platform.
And fighting it meant seeing clearly, knowing what I was watching and telling the truth about what was happening. It brought the golden rule of journalism into clear focus for me: objectivity. I understood then that objectivity means giving all sides a fair hearing, but it doesn't mean treating each side equally.
Objectivity does not mean treating victim and aggressor the same. Objectivity doesn't mean ascribing a false moral equivalence. But that's what our governments were trying to do.
Those officials from the United States and across Europe who didn't want to intervene to stop this were saying all sides are equally guilty when they weren't. And the massacre at Srebrenica finally proved it, finally proved our governments could no longer look away.
A year before Srebrenica, as the Bosnian War still raged, President Bill Clinton came to Atlanta to participate in a CNN-hosted global affairs forum. I was one of several correspondents stationed around the world for something like a global press conference.
The moderator, our anchor Judy Woodruff, brought me in for a question from Sarajevo. I hadn't thought of, or planned it, as a confrontation. The President had been speaking about the great job America had done in providing humanitarian assistance, and I was finding it hard to stomach.
All I could think of was "never again, never again."
I asked a long question -- I remember it like it was yesterday -- why all the "flip-flops" on Bosnia by his administration, why not stand up to the Serbian war machine, and wasn't he afraid of setting a dangerous precedent?
I made him angry. It was an awkward moment for me. It was probably an awkward moment for the President, but in hindsight, I think I did the right thing. We were in the pre-viral age, but this encounter ricocheted around the world.
It was a serious and dramatic question about why the world wasn't doing anything to stop a genocide.
I wish that the world would get as serious about defeating ISIS -- as it eventually did about defeating the genocidal Serbian strategy back in Bosnia at the end of our bloodiest of centuries.