The empire that officially ended in 1918 after World War I was the Austro-Hungarian Empire. The collapse of this multi-ethnic empire resulted from military defeat and political disintegration, culminating in the establishment of several nation-states in Central and Eastern Europe. Created through a complex system of alliances, it crumbled following the war, leading to the Treaty of St. Germain in 1919, which formalized its dissolution. This transformation not only reshaped the political landscape of Europe but also contributed to various ethnic tensions and conflicts, setting the stage for future geopolitical challenges in the region.