As the tin says. Something I like about allohistorical scenarios is speculating on the survival of polities that, well, didn't. For instance, the Habsburg monarchy lasted centuries in Central Europe (compared to a measly two centuries in Spain), but underwent reversals in the 19th century and ceased to exist as a notably entity shortly after WWI. So, what was the point where it was all over for them? Francis I's death leaving the throne in the hands of an ill-suited heir? The Spring of Nations ending Metternich's luck? The accession of Franz Joseph, a stubborn rock in a rapidly changing world? The death of his heir Rudolf? Or was it the assassination of Franz Ferdinand, which lit the bonfire of the world? (Other countries like Alexander's empire are welcome to be discussed as well).