Why were Austria-Hungary's Slavic minorities put into multinational states?

Effective political lobbying and influence by political activists by the Czechs and the Yugoslav committee.

http://en.wikipedia.org/wiki/Yugoslav_Committee

Both Yugoslav Committee and the Czech already had the ear of important people moving into the Paris conference.

I wonder if it sheds any light on this decision if we compare the examples cited above with the one instance where the opposite happened- Galicia?

Poles and Ukrainians were intermixed to a degree that would induce a headache in anyone trying to draw a "fair" borderEthnic Map of Poland (for the purposes of this discussion please consider "galicia" to be roughly the southern 3rd of the 2nd polish republic this map is of course a simplification, Ukrainians lived in small villages as far west as Biesczady and scattered Polish settlements existed in the countryside throughout Galicia even prior to 1920 - ie: before the Polish government gave farmland to settlers.

but broadly there was a pattern of Polish majority urban centers surrounded by 97% ukrainian countryside- making absolutely impossible to draw a viable state border based on ethnic criteria.

in this case Poland & Ukraine fought a war over East Galicia, Poland won but Many Ukrainians were never reconciled to living in a Polish state. Ukrainian insurgents mounted operations in South East Poland in the interwar period. the Polish government responded with, alternately - short lived experiments in autonomy/toleration & heavy handed "pacification". the spectre of the Holodomor lead to a rapprochement between constitutional Ukrainian parties and the Polish Government but this came far too late and was soon rendered moot by ww2 and the destruction of the Polish state by Nazi & Soviet occupiers.

the new occupiers were easily able to play on ethnic hatreds between Poles & Ukrainians and the legacy of ethnic conflict finally burst into the open when unimaginable blood shed was unleashed in Wolyn & Galica in 1943-44

The apparent reason for the creation of these Slavic "multinational" states was to create states that were strong enough to act as "buffer states" against Austria, Hungary, and Bulgaria (Germany's allies in World War I).

Czechoslovakia, Yugoslavia and Romania would, in fact go on to form the "Little Entente", with which France later formed an alliance.

So these states were probably created for reasons of Realpolitik, not to benefit the "nationalities."

Retrospectively, the only answer to your question is: "because of poor grasp of the local political and cultural context".

In the 1920s, dominant countries were organized on the notion of nation state. This was a relatively recent development; for instance, Germany had formally existed only for 50 years or so at that time. Other countries had turned into nations somewhat earlier; e.g. France converted from loose feudalism to nation over about five centuries (from the first attempts at bureaucratic centralisation under Philippe le Bel to Napoleon's nation-building epic). Crucially, some peoples had not, at that time, completed or even began their nation-creation process. This is in particular true of areas which had long been part of empires, in this case Ottoman and Austro-Hungarian.

To a large extent, a nation can be created only through events which define it in the psyche of its individuals; such events must impact all or most of the future nation's population, but exclusive of others; that exclusivity is what makes the nation. In the context of empires (which were the norm throughout history, before modern times, for large scale political constructions -- read John Darwin on that subject), nations thus rise through resistance to a conquering empire, or emergence of a local leader amid the chaos of a disintegrating empire. There is no sure-fire method for creating a nation, but it seems reasonable to state that nations could not develop and flourish while within the boundaries of functioning empires. The decline of the Ottoman empire had allowed proto-nations to begin to form but (as yet) this process was not complete.

Yugoslavia was the result of the unification of several provinces taken from both Ottoman and Austro-Hungarian empires, a concept which was based on the (flawed) ideas that:

• Nations are large and must cover a "decent" area and population. No micro-state !
• Nations correspond to the then-popular notions of "races" which can be approached through linguistics.

In that sense, the WWI victors pushed for the creation of a single state of Yugoslavia: Serbia, Croatia, Montenegro... could not be nations on their own (too little), and there was no problem in putting all of them in a single country since they were all "South Slavs". This kind of myopia, when it comes to defining post-WWI borders, is famously illustrated by the 14 points of Woodrow Wilson, who, from Washington, could idealistically rant about the necessity of adjusting frontiers "along clearly recognizable lines of nationality."

As for Czechoslovakia, a similar process implied grouping areas based on language, but other forces were at work too. The Czechoslovak Legion fought along with the Allies so as to secure independence after the end of the War, with as big a territory as possible; e.g. inn 1919, Czechoslovakia and Poland fought a small war over some disputed areas.