Sending troops to support NATO allies on the Russian border is a good idea. Also, our quick response team groups would be more effective. Obviously, this should only be by the request of those countries. Poland, Estonia, Latvia and Lithuania should not subject to Russian troops entering their countries in plain clothes, as in the case in the Ukraine.
That being said, no country is likely to send their troops to the Ukraine to help.
I am thinking that this war is begining to look like it will be a proxy war for quite some time. The ethnic Russian Ukrainians (the rebels) are unlikely to matter to Putin if any get killed and the NATO nations will probably be content to just supply the arms to the Ukrainians. The special forces of both Russia and NATO countries will almost certainly be unofficially involved and in the case of Russia perhaps some of their own regular forces as well on a covert basis, if any of these get killed, or captured the various governments will simple deny that that they are anything to do with them.
Like Vietnam, it will be a war of attriction with lots of people coming home in body bags. At least some of the numbers on both side will be made up with mercenaries, more than likely on both sides. This will be an economically very costly war for Ukraine, so a lot of the funding will be supplied by the NATO countries for mercenaries and other things. The Russians have plenty of older equipment which will be surplus to any important requirements, so their costs of this war might not be particularly burdensome.
As in Vietnam, America eventually was fighting a war, which was unpopular at home and the war was a severe burden of the American government. Added to that The American government were going to need to intensively bomb the cities of North Vietnam to beat the North Vietnese, which was already becoming very unpopular around the world at that time. As time goes on public opinion makes life very difficult for democratic nations fighting such a war. Eventually it all gets too much and they will want out and terms will be sought.
Like the Vietnam war, proxy wars are likely to become the opportunity to use use banned weapons and normally unacceptable methods, mainly because the major powers find ways of denying involvement, or responsibility. Also although both sides don't like to admit it, proxy wars are a useful oppotunity to test new weapons and new tactics. Weapons and weapon systems which have been proven in combat are much easier to sell and many customer countries will be keen to buy the latest proven weapons.
Although everyone is saying that they don't want this war, the present financial situations in many of these countries are not as good as they would like and a coming proxy war will help them to sell arms and weapon systems to boost their economies. I can't speak with much knowledge about other countries, but the UK (my own country) has a very substantial arms weapons development and manufacturing industrial sector.
A lot of this situation may be all about making money and it could be a crazy amount of money as well, so perhaps some big incentives are also driving this present situation. Older military equipment which is overdue for replacement is a lot easier to find buyers for, if there is a war somewhere and major powers will be well interested in selling of older weapons, added to that weapon sales nearly alway create follow on business opportunities as well.
Companies get contracts to develop upgrades for older systems and everyone is going to be very happy while this situation is ongoing. Meanwhile the rest of the world is getting into debt, buying all these weapons which they can't afford and many of the countries involved in the arms trade will also be those who lend them the money.
