The approximate cause is the spate of bombings in Russia in September, universally assumed to have been planted by Chechen "terrorists". But there are deeper reasons - above all Moscow's desire to control its southern marches, and to keep the Caucasus, gateway to the energy riches of the Caspian and Central Asia, within its traditional sphere of influence.
The Chechens are Islamic. So re the insurgents Islamic extremists?
It is true mercenaries and financial assistance have come from countries like Afghanistan, Saudi Arabia and Pakistan. But the brutal onslaught is likely to merely unite moderate and radical opinion, making nationalism rather than militant Islam the key factor.
Who is calling the shots in Moscow?
The generals, out to avenge their humiliation in the 1994-96 war, which led to de facto independence; and the Prime Minister, Vladimir Putin, whose approval ratings have soared as a result of the fighting.
But if the West acted against Serbia over Kosovo, why can't it act against the Russians over Chechnya?
Good question. The simple reason is that Serbia is a minor power while Russia, however diminished its military might, remains the world's second nuclear power with right of veto at the United Nations and much mischief- making capacity on the global stage.
So is there anything the West can do?
In all honesty, not much. Economic sanctions, could backfire by triggering loan defaults or a repeat of Russia's 1998 financial crisis that might destabilise international markets.
What about diplomatic retaliation?
Again, beyond gestures, there is little that can be done. Russia could be suspended from membership of the Council of Europe, and the West could refuse to sign the new European Security Convention, which is supposed to be approved at the 18 November summit of OSCE, but which Russia is violating with its military build-up against Chechnya.
Could the war spread?
Possibly, if the Chechen guerrillas start operating out of the neighbouring countries, Georgia and Azerbaijan, and the Russians carry the war there. But this is unlikely, given the physical barrier of the Caucasus mountains. The most immediate risk is that a massive flow of refugees will destabilise tiny neighbouring Ingushetia.
How long will the Russian onslaught last?
Don't expect an early knockout. The first Chechen war lasted two years. This one, a war of attrition and aerial bombardment designed to minimise Russian casualties, could last just as long. Winter is coming, and the Chechens are masters of guerrilla warfare.
So what is the best hope of ending the war?
A change of heart by ordinary Russians. There have been some signs the public is starting to feel that the use of force is disproportionate, the humanitarian misery unacceptable. If pressure builds, Boris Yeltsin and Vladimir Putin may then be obliged to seek a negotiated settlement.