It all began with the break up of the old Yugoslavia.
Unrest in Kosovo was followed by declarations of independence from ethnic Albanians - something Belgrade flatly rejected. By the late 1990's the former-neighbours were in open conflict. Belgrade begun ethnic cleansing, forcing civilians to flee across international borders in their thousands.
By September of 1998, NATO feared a humanitarian crisis on its own doorstep. The Serb President Slobodan Milosevic was warned to stop - he declined, and efforts to broker a truce faltered.
So NATO sought a military solution. It launched wave-after-wave of airstrikes, despite never obtaining a mandate from the UN Security Council.
Serbia's major cities, Belgrade and Novi Sad, bore the brunt of the 78 day assault.
That intervention, known as Operation Allied Command, would dominate news reels. Jamie Shea was NATO spokesperson at the time. Twenty years later, he recalled his enduring memories of the 11-week campaign.
"The intensity - it lasted 78 days, which by the standards of modern conflicts which seem to go on for ever and ever, was amazingly short. During that time, those 78 days, the Kosovo story was really that number one international headline, and therefore we had 400 journalists permanently camped out at NATO headquarters with round the clock press briefings."
He added, "my abiding memory of the time was simply the intensity and the need to have this constant flow of updates and information to supply the needs of the media."
"Secondly thing was the uncertainty. You’d think that one day’s things were going very well, that we were getting our story across, and convincing public opinion that NATO was doing the right thing, and then you’d have an incident of this so called collateral damage, like the accidental bombing of the Chinese embassy, things that nearly everybody remembers and you would feel that the stone had rolled its was back down the mountain and you had to start that public relations work all over again."
Twenty years on, he continues to defend the operation, and the wider concept of humanitarian intervention.
"The ethnic cleansing was stopped, and so there are good interventions. I think the 20-year-anniversary is a moment to remember the international community can do good."