I am aware of what happened to Germany, their Spring Offensive failed, leaving the allies to either march into Germany or sign an armistice, and the latter occurred in the Treaty of Versailles, which started a slippery slope into the Second World War.
It seems that all the history lessons I have had on the actual war itself and the end of it involves only France, Britain and Germany. I have no idea of any major battles involving Austria-Hungary since the Russians left the war in 1917.
What I certainly don't understand is how they disappeared off the face of the Earth at the end of the war. I know that there were several ethnic minorities around Austria-Hungary at that time, do they have anything to do with it? Or was it just another clause in the Treaty of Versailles?
With the rise of nationalism and the concept of a "nation state" during the mid-19^th century there were obvious tensions between the different nationalities and mainly against the "oppressive" absolutist government in Vienna. These tensions were amplified by the fact that the Austrian Empire included so many different groups compared to other Empires like Germany or France.
In 1848 revolts rose up all around Europe and the Hungarians happily joined in, to a degree that it took support from the Russian Army to eventually win back Budapest. Still, something had to be done so to appease the largest single minority in the Empire the Kaiser in 1867 eventually agreed to split the country into a dualistic monarchy joined together mainly by the crowned head of state.
The two halves still shared a currency and tolls and three joint ministries (foreign relations and defense plus a treasury to supply those two); other than that the Hungarian Diet and the Austrian Reichsrat were practically independent entities.
Of course this mainly placated the Hungarian concerns, there was still a large Slavic population that felt generally unrecognised and at least partially repressed (moreso in the Hungarian half), which is why the Archduke Franz Ferdinand was seriously considering another Ausgleich like in 1867 to form a third state for the South Slavs.
Anyway, if we jump to the war we find a lot of support for it everywhere in the Empire. Catchy slogans were widespread, such as Serbien muss sterbien ("Serbia must die" but deliberately written wrongly to rhyme) or Jeder Schuss ein Ruß, jeder Stoß ein Franzos, jeder Tritt ein Britt ("every shot a Russian, every thrust a Frenchman, every kick a Brit") but as the war went worse so did the morale.
In 1916 the neo-absolutistic Kaiser Franz Joseph I. died at over 80 years of age and his grandnephew Charles succeeded him. He immediately tried to negotiate peace for his own, already badly battered Empire but at that point the show was essentially run by the German war council.
It's too late for Austria-Hungary anyway. In May of 1917 the parliament convenes for the first time since the declaration of war. War-tired minorities of all sorts immediately use this platform to proclaim their desire to break away, Galicia wants to re-join Poland, the Bohemian Slavs want their own state and the Slovenians and Croats want to join Serbia in a united Slavic state.
When, in late 1918, Entente attacks eventually break the western front to the point where even the German war council wants an immediate ceasefire the Austro-Hungarian minorities see their chance. Desertion is already rampant, with whole battalions and divisions simply going home without orders so it's not like the military luck is going to improve again.
Seeing the utter destruction of his Empire imminent, on the 16^th of October Charles publishes his Völkermanifest, his manifesto with which he tries to encourage the formation of a federation of states from the former Austrian half under his guidance (Hungary already being regarded as completely lost); it's not regarded well. 5 days later the German members of the Reichsrat in Vienna come together to form the provisional assembly of Deutschösterreich. While they still debate their own issues, the Empire is coming down around the former capital.
On the 24^th Hungary declares the union with Charles dissolved with the end of the month; Charles signs it because in the end it's not like he can stop it.
On the 28^th the assembly in Prague takes over and proclaims their independence as Czecoslovakia. On the same day, Galicia officially detaches to go back to Poland.
Just a day later, Croatia and Slovenia join Serbia to form a South Slavic state.
On the 31^st Romanian Siebenbürgen joined the Romanian Kingdom.
Only on the 3^rd of November did the first armistice get signed (Villa Giusti), so these things all happened before any demands of the Entente could be brought in. The actual territorial losses demanded by the allies in the Treaty of Saint Germain were few, the biggest forced land ceding was probably the German-majority area of Southern Tyrol south of the Alps, which Italy demanded mainly for tactical reasons. The treaty mainly forced Austria to accept the integrity of the new nations and helped define the borders between them.
I'd also like to point you towards this old post of mine, which goes into a bit more detail on the dissolution of the monarchy in particular.
The TL;DR of this is that the Austro-Hungarian empire was held together by a thread before the war.
Back in 1868, the Austrians had granted Hungary status as its own Kingdom, with its own Parliament, etc - rather than being one government, the Empire was transformed into a personal union of crowns, where the Austrian Emperor was also the Hungarian King.
The Hungarians actively worked against the Austrians (and, for that matter, the crown) during much of the period after that - their actual goal was independence, and they were very, very good at working within the system to frustrate the system.
When Imperial authority collapsed, there was basically no question of trying to put the beast back together. The Hungarians wouldn't stand for it, and neither would the Czechs (who had their own seperatist movement within Austria).