Don't encourage them

 When Russia decided to invade Ukraine I was one of those who did not expect the conventional war to last more than a few weeks. The commitment of the Ukrainian defenders - and the intelligence they've shown - has been inspirational. Sure they've been given a lot of weaponry by other countries, but the Afghans have just finished showing us that all the weaponry in the world won't help if an army isn't willing to fight.

More than just delaying the Russians, Ukraine's bravery allows everyone else the opportunity to provide more help. There's time to train on new weapons; we can be confident they will not just be handed over to the Russians (indeed, weapons given to the Russians seem more likely to end up in Ukrainian hands than the reverse).

And make no mistake - it is in everyone's interest (including most Russians, ultimately) for the invasion to be an expensive failure. A world where such an unjustified war of conquest is repelled with help from many other countries, is a safer world for us all. Let the next autocrat think very hard about invading a neighbor for whatever reason; let them worry that the whole world may gang up on them. As well as the Ukrainians are doing, the whole thing is a mess of death and destruction.

But there's worse to Putin's aggression here than just this war. A long time I go I was critical of the US invasion of Iraq because (among other things) it encouraged other countries to get nukes. If the US accuses you of trying to build them, you either open your pockets like Iraq and get invaded, or test one and tell everyone to go away like North Korea. That's bad, but it's limited. It's a defensive move (at least by example); and the US gave no hint of using its own.

By contrast Russia gave Ukraine guarantees of territorial integrity in exchange for giving up nuclear weapons. They have now broken this agreement and invaded. In addition, they threaten (in not-so-subtle ways) to use nuclear weapons if others intervene or if they appear to be losing in their illegal war of conquest. The message this sends to others is very clear: you cannot trust anyone else to leave you alone; get nuclear weapons. And worse: if you have nuclear weapons you can invade your neighbors with impunity.

However true these things may have been before in theory, we now have a clear example to point to. If Russia's invasion is a success by any measure, it will set a clear precedent that no country can ignore. But if the world bands together to repel it that will also set a precedent - for peaceful countries that they need not acquire their own weapons, and for autocrats that they will not be worth the expense and opprobrium.

The result of this war will have a huge effect on the world of the future, and in working out our response to it all the risks of proliferation should be included in the scales.