I take the freedom to dump a text from my blog here, since it relates to the topic. The properly formatted version is here.

Putin's approach to aggressions is an interesting one. It appears he
has recognised the limitations of his freedom of action, found and began to
exploit loopholes.

An all-out conventional invasion, 1914-style, is apparently out of question to
him. Russia lacks the forces to pull this off on a grand scale, at least without
exposing itself too much.
His exploits appear to range up to army corps size instead (South Ossetia
2008) - with all other power being held in the back, as a political equivalent
to a "fleet in being". This restricts the freedom of action of other great
powers. Small powers can probably not pull off the same risky games for they
lack this component - even if they could easily muster forces equivalent to
the ones employed actively.

Traditional Cold War deterrence rested on the fear that a too bold move
might lead to World War III, and the demise of European civilisation. There
were no aggressive moves done in Europe proper after the Berlin blockade;
both blocs were content with keeping their own line*. Bold moves were
largely restricted to Asia, with proxies and at times small numbers of
opposing great power troops fighting against each other**.

There as a fear that some bold, yet incremental, moves could be dared in
Europe - and it was difficult to define when exactly such incremental
offenses should lead to mobilisation or war. A British satire (a "Yes, Prime
Minister!" episode, see 7:04 minutes and after) explained this better than
articles or books ever did. Also remember the metaphor of boiling frogs.


Putin appears to have thought of this incremental approach when he decided
to send paramilitary troops without national insignias into the Crimea.


He did apparently also take into account that the Ukraine is not allied with
any country.


Finally, the third ingredient; international law had been stretched somewhat
prior to the move.


Putin did stretch his freedom of action in face of International Law
proponents prior to the conflict with Georgia in 2008 by exposing
'peacekeeper' troops. Georgia proceeded to attack South Ossetia at some
point and this included firing on peacekeepers. At that point Putin had a
semi-plausible excuse for intervention. His intervention was not as blatant as
the intervention of Kuwait 1990, for example. Him withdrawing after fait
accompli avoided troubles as well.


The stretching of International Law for the invasion(s) of the Ukraine wasn't
done by Putin himself. This damage was done by Western great powers which
had a fit of arrogance and short-sightedly decided that rule of force suits
them better than rule of law. Rule of law was supposedly a concept to be
applied on other powers only.

Except that the "other powers" includes some great powers which evidently
can behave arrogantly as well.

2014-02 Hypocrisy in effect

It would help if the same Western great powers reaffirmed the importance of
international law in a non-hypocritical way. They could admit guilt, seek and
accept a ruling about compensations and - most importantly - refrain from
further violations.

This won't happen, of course.Only losing aggressors have to show regret in
this world.

Another approach to close the loopholes would be to expand the collective
defence systems; offer an alliance of some kind to the Ukraine. This is most
unlikely as well. It would lead to further conflict and might end up being
much too expensive. The Ukraine is not too big to fail, after all. Nothing in
there is really crucial to the West (for historical reasons), while much in there
is crucial to Russia.

Finally, one could tune up the reaction to incremental moves and effectively
turn incremental moves into too big moves thereby. This appears to be the
preferred approach among Western great power governments.