The reasons were moral - to end the suffering of the Kosovo Albanians - and strategic - to stabilise the Balkans.
While there was an element of political calculation, the consistency with which he represented the decision always suggested a more personal commitment reflective of his temperament and generation.
He has had an ambivalent relationship with the military since his first presidential campaign, when documents suggested he dodged the Vietnam draft. He rarely looks comfortable addressing military audiences and his salute still looks unconvincing.
Perversely, perhaps, his lack of experience may have given him something to prove, and he has resorted to force more than any recent president - helpedby the end of the Cold War, which removed the risk of precipitating a superpower conflict.
In Kosovo, though, there appeared also to be three other factors. First was his sense that if Yugoslavia could be pacified, the last source of instability in Europe could be removed, leaving the continent with a durable peace: that would be a legacy this legacy-conscious president could claim when he left office.
The second factor was not to repeat the mistake of leaving intervention too late, as he believed happened with the break-up of Yugoslavia and Bosnian civil war. The third, common to the new generation of European leaders, was a grander ambition: to end the 20th century by demonstrating that nothing like the Holocaust could happen again, because the next generation of leaders would not flinch from meeting force with force. Transformed into advocates of limited force, the likes of Bill Clinton have resurrected the just war, a concept their anti-war campaigning qualifies them uniquely to embrace.