A concentrated nuclear war would not be the end of all mankind. But it still ought to be considered a sufficient risk that would prevent France and NATO to stop sending troops to attack Russian soldiers. And besides the unstated principle here is that Russia considers this war to be justified. And though no one in the West cares to take that into consideration, still it is what Russia thinks. Not just because of Ukraine always being a part of the Russian Empire, but also because the criminal elements have taken over. You can not really see this from the West, but if you have ever been there, you know exactly what I mean.
In fact there is no such thing as one united Ukraine. Anyone can tell you that there are two distinct Ukraines. One is the well known bandits --the people that have theft and murder deep inside their DNA. The other are the vast majority who are close to angels in their good character. The trouble is that it is always the bandits that get the power and control. Thus without Russian rule the place becomes a nightmare even for the average Ukrainian. This is the reason even the churches there need armed guards. There is just a bit too much of the wrong kind of element.
