While the precise cause of the explosion may be in dispute, the significance of this sudden, violent transformation of what was intended as a "hearts and minds" mission to win over the local population into a provocation igniting mass anti-US protests is clear.
It is a telling expression of the mounting popular hostility to foreign occupation and the growing crisis confronting the US military as the Obama administration embarks on its 30,000-troop escalation of the eight-year-old war.
The worse these bombing attacks get, the more radicalized those left standing will become against the US/NATO occupation.
You cannot murder people's children, and expect that they will welcome you with flowers.
Those at the Pentagon who have signed off on the indiscriminate bombing of civilians in Afghanistan haven't quite gotten that bit straight, apparently.