"The Bosnian crisis of 1908–09, also known as the Annexation crisis or the First Balkan Crisis, erupted when on 6 October 1908, Austria-Hungary announced the annexation of Bosnia and Herzegovina, territories formally within the sovereignty of the Ottoman Empire. This unilateral action—timed to coincide with Bulgaria's declaration of independence (5 October) from the Ottoman Empire—sparked protestations from all the Great Powers and Austria-Hungary's Balkan neighbours, Serbia and Montenegro. In April 1909 the Treaty of Berlin was amended to reflect the fait accompli and bring the crisis to an end."

https://en.wikipedia.org/wiki/Bosnian_crisis

There is no way you can honestly argue, after reviewing the facts, that Bosnia was NOT annexed by Austria. Btw I am from Austria and here we are taught the same thing in public schools. Austria unilaterally annexed Bosnia. Bosnian nationalists then assassinated crown prince Franz Ferdinand which then was followed by the first World War.

That is why Austrian Empire was torn into pieces after the first World War and why it was deemed the aggressor and had to pay crippling reparations.