The extremists – who probably number between 5,000 and 10,000 and include local Pashtuns from the Pakistani Taliban, Uzbeks, a few hundred Arabs and even some Western volunteers - know that they are now engaged in an existential battle. So does the Pakistani army, which has deployed around 30,000 men backed by tanks, helicopters and artillery.
Previous operations in the restive semi-autonomous South Waziristan tribal area have ended in widely derided peace deals which have left the militants' power largely untouched and the army's prestige battered locally and internationally.
The first was in 2003 and since then the frontier zone has become a globally recognised haven for extremists including Osama bin Laden and his al-Qaeda group. It was in South Waziristan that the 7/7 bombings were conceived and, to an extent, organised. It is from here that, Pakistani officials believe, three quarters of the bombings that have hit their cities in recent weeks are masterminded.
Both sides now know that this time no deal is possible. If the militants succeed in holding off the military - or in causing so much mayhem around the country that the assault is halted - then they will have defeated the most powerful institution in Pakistan. This will almost certainly force a political crisis, possibly a coup.
For the Pakistani Army, only outright victory will prove their capacity to defend their increasingly sceptical countrymen and to convince a dubious USA of their resolve to act against extremism.
But beyond this, things get more complex, as with all current conflicts. To get at the Pakistani Taliban, the Army is relying in part on the cooperation of various other militant or tribal factions. Raj frontier administrators might have approved but the international community is more particular these days.
