Tanystropheus42:
First of all, I need to explain something. When I read the challenge, I decided to not just show the secondary power (in this case, a surviving reformed Austria-Hungary), but the power that overshadows it (Germany). So, I created a map of Austria-Hungary with some exciting new internal divisions, then moved on to Germany, then did the rest of Europe in shot. I then made one worlda showing the political situation in Europe and another showing allies/spheres of influence for the Great powers. Then, I realized that I had gone a little bit too far.
I got caught up world-building essentially, which is why the map(s) show a little more than the challenge specified.
Sorry if its a bit long.
(Extra note, because the maps don't overlap and the change in the last one was unspecified, I decided that this map is set in the same universe as my last MotF entry.)
Anyway, here's the map;
When he learns that the other assassins have failed, Gavrilo Princip decides to drown his sorrows instead of taking the proactive course he took in OTL. The assassination attempt is remembered as little more than a footnote in history. The Great war had been delayed, but Europe in 1914 was still a powder-keg. The various treaties and obligations between the powers meant that if war was declared, it would likely spiral out of control.
The crisis came three years later, in 1917, when Serbian nationalists managed to kill the Austro-Hungarian governor of Bosnia. Two days later, in an unrelated incident, the Austro-Hungarian ambassador to Serbia was shot in the street. In the diplomatic confusion that followed, Austria declared war on Serbia, which led to a chain reaction as the various powers were forced to declare war in support of their allies.
I'm no expert on military history, so I'll keep it brief. The UK decides to remain neutral (though pro-entente), while Austria-Hungary is forced to hand over South Tyrol and Istria to Italy, to keep the Italians on side. Belgium is effectively partitioned when both Germany and France try to pull a Schlieffen plan on each other. The war settles down into 5 years of brutal trench warfare, punctuated by occasional pointless assaults to try and achieve a breakthrough, that invariably achieve nothing. The Spanish Flu pandemic in 1918 only serves to make conditions even more hellish. Austria occupies Serbia and Montenegro, while Bulgaria reclaims irridentia lost in the second Balkan war. Romania stays neutral before trying to invade Transylvania in 1920, followed by their rapid occupation and capitulation. Russia sees defeat after defeat, then inexorably descends into civil war.
The war ends in 1922, in a crushing Entente defeat. Peace is signed with Russia when the Germans agree to help the fledgling Russian republic against the Bolsheviks. In return, the Russians don't complain when the Germans carve a wall of buffer states from Western Russia, imposing German monarchs on many of them. France gets a really harsh deal; Italy annexes Savoy and Nice, while Germany occupies the Northern industrial and border regions in Picardy and Burgundy, and takes a large share of the French colonial empire for its own. Austria puppetizes Montenegro and Serbia.
A short civil war sees the French left rise up and try to establish a workers republic. The revolution is crushed swiftly, and drives the already conservative government ever further to the right. They even try to reestablish the French monarchy.
The 1920's are mostly a time of rebuilding throughout Europe. Italy went fascist (what, they were on the winning side and went fascist OTL, why can't it happen here as well?), eventually settling down as a virulently nationalist, belligerent semi-rogue state. Germany reforms during the 20's, stumbling into true democracy (Wilhelm "walking diplomatic indecent" Hohenzollern managed to convince the German people that maybe constitutional monarchy wasn't such a bad idea after all). Russia stabilized as a conservative, semi-democratic republic.
Seeing the other nations of Europe reform spurned on protesters and campaigners in Austria Hungary to pressure their own government to do the same. The first compromise was to elevate the Slavic lands in the south to the level of kingdom, starting the triple monarchy phase. Despite many failings, this worked well enough to keep the empire together through the 20's.
The 1930's were... tense.
The great depression ruined economies across the continent, unleashing a new wave of violence on an already battered land. Britain, Germany and Russia weathered the storm fairly well, along with a few select allies, while the rest of the continent slowly collapsed into anarchy.
Austria-Hungary-Slavonia gradually descended into chaos. As unemployment rose, and as standard of life fell, formerly contented minorities started to turn against the status quo. There were never any outright rebellions, but riots were common, and the central government lost control of large areas of countryside. In areas where ethnicities came into contact or were mixed, the situation was even more complex, as sometimes centuries old feuds were reignited. Nevertheless, given time (and a little German military help) the Empire pulled through.
Elsewhere, the Greek monarchy was abolished when a cabal of military officers staged a coup and declared a republic, while Albania was puppetized by Italy, and Romania slid inexorably into fascism. Iceland and Greenland declared independence from Denmark after some new poorly thought out heavy-handed regulations were introduced in 1939. Belarussia saw 6 attempted coups in under 4 years, while the doomed German project to create a United Baltic Duchy imploded spectacularly, leading to the creation of both Latvia and Estonia.
The French regime effectively dug its own grave, pouring men and resources into a pointless colonial war trying to keep hold of Indochina (Vietnam became France's ... er ... Vietnam) while simultaneously ruthlessly cracking down on dissent. This was the perfect environment for the remaining French communists; inspired by the concurrent Brazilian and Nova Grenadine revolutions in the Americas, France fell to a second revolution in late 1934. The regions Northern France under German occupation hastily proclaimed independence from France as the republics of Burgundy and Picardy, and sought protection from Germany. This led to a very tense standoff between France and Germany that nearly sparked war (fortunately, cooler heads prevailed). The Spanish civil war happened right on cue (even spilling over into Portugal), and French meddling was key to the eventual communist victory.
The continent that emerged from the 30's was a changed one. Germany and the newly resurgent Russia created a new defensive treaty to guard against the threats posed by fascism and communism, drawing in many of their allies into the new "Eurasian Common Defense Treaty", including an Austria that got pulled along for the ride. Russia proved its newfound strength in the second Russo-Japanese war (1943-1947) that saw the Russians dismantle the Japanese colonial empire in Asia, and replace it with a string of new, Russian aligned states. A cold war gradually materialized between the democracies and the communists, with the few fascist states left slipping into North Korea style impoverished dystopias.
The Late 40's saw another round of reform in the triple monarchy. When the dust settled and order was restored, it was plain to see that the old system had failed. The new constitution agreed in 1948 saw the state rearranged as a federation of autonomous kingdoms and duchies under one crown (Austria, Bohemia, Carniola, Croatia, Dalmatia, Galicia, Hungary, Krakow, Slovakia, Szeklerland, Transylvania and Vojvodina), and with Bosnia as an "autonomous associated state" (ethnic violence got particularly bad there in the 30's and it was quickly realized that any attempt to partition the region would create more problems than it solved. Bosnia thus remained neutral ground within the new federation). Later, in the early 50's a series of new autonomous regions were added to represent the distinct regions within kingdoms that didn't have a large enough population to form Kingdoms of their own. This form of government has persisted, with a few minor changes, right the way to the present day.
In 2017, the Danubian Federation (as it is now called) remains a great power and key player in the region. Its economy is booming, tech startups are flourishing and people are generally happy with their government. Serbia and Montenegro have transitioned from puppet states to loyal allies, while Istria fell into the Danubian sphere of Influence after it broke away from the collapsing Italian fascist regime in the 80's.
But despite all this, they are still overshadowed by their more powerful neighbour to the north.