World War One was shorter, earlier and much less devastating than in OTL. The old system which held sway over Eastern Europe since the end of the Napoleonic Wars, shored up by the power of Austria and Russia, came to an end. The succeeding years saw both chaos and consolidation, as revolution swept the Balkans and Russia and as Germany became a great power.
World War One
For more details, see the main article about this subject. Most pre-war observers considered an Austro-Russian victory likely. To their surprise, Austria collapsed quickly and though Russia proved harder to subdue, the Allies won a (relatively) quick and easy victory, and thus did not harshly punish the losers.
The Post-War OrderUnrest forced both Austria and Russia to reform: the old Austrian Empire, under threat of revolution, morphed into Austria-Hungary, and eventually the United States of Greater Austria. With the last change, the long-reigning Franz Joseph abdicated in favor of Franz Ferdinand. The new emperor reminded many of the old councilor Bach: liberal towards the ethnic minorities but a staunch Catholic, fearful of war with the great powers but in favor of expansion overseas.
The Balkans found themselves divided again between Britain and France, along the same line as Austria and Russia did. The Balkans states furious at their 'betrayal' by Russia during the war, assembled armies in secret, to fight for complete and total independence.
The Revolutions of 1899-1906
China had long suffered under the colonial yoke and the post-war Japanese occupation of Manchuria only increased the number of secret anti-Western societies, often supported by the Qing government. In 1899, the most important of them, the Yihetuan, or Boxers, launched a large uprising in Northern China and Manchuria. Though the Europeans eventually crushed them, the Boxers threw back numerous relief expeditions.
The Ottoman Empire gained little in the Balkans from the peace settlement, as well as taking awful casualties in the Caucuses front, and the British added insult to injury by annexing Cyprus. The Yihetuan victories, though ephemeral, inspired a secret group of army officers, The Young Turks, to launch a coup against the sultan, which succeed. Egypt also saw nationalist uprisings.
With the British and French distracted by the Young Turks, the Balkan nations saw their chance and revolt broke out everywhere. Besides the anti-British and French revolts, numerous ethnic conflicts occurred, and internal governmental conflicts occurred in both Serbia and Greece.
By and large, the most significant events occurred in Russia. Alexander IV lost his throne and fled to exile in Sweden. The revolutionaries established the Russian Republic, despite a few radicals pushing for socialist revolution. The Republic, however, tumbled into crisis as seemingly every ethnic group in the empire pushed for independence. Poland, Finland and Romania invaded to try and grab land and support the large Ukrainian insurrection (also aided by the British). The Germans also (secretly) sent troops into the Baltic states.
The British and French moved quickly to crush the Young Turks and the Balkan revolts, and despite several reverses, succeeded in restoring the old order. Not so in Russia. Franz Ferdinand called an international conference to prevent an all-out war over the spoils of Russia. The British gained the most, with the creation of a large, independent Ukraine and the independence of the Mountainous Republic of the Northern Caucuses (MRNC), both states beholden to British interests, while French-aligned Poland got huge swathes of land as well. Germany only got Courland and a puppet state in the rest of Latvia (though Estonia and gained independence as a Russian vassal).
Humiliated, Germany laid the groundwork for an alliance with Finland, as well as annexing the three Thuringian states. Near the end of the wave, Mexico sunk into its prolonged and bloody revolutionary conflict, and republican elements overthrew the Qing, leading to the independence of Mongolia and Tibet.
Many other states saw failed or abortive uprisings: