Oh, I can think of several. The rise of Alexander the Great, which put an end to all experiments with democracy in the Hellenic world. The overturn of the Roman Republic. The consistent and complete defeat of the slave rebellions in Sicily and Italy. The feudal counterrevolution in 13th- and 14th-century Italy (you won't see any more of that bourgeois rule crap!) The English Restoration of 1661. The Congress of Vienna, which pretty much put an end to the ideology of the French Revolution. And where did Radical Republicanism go after 1876?
In any case you have to distinguish between defeats suffered by classes, parties, governments; and refutations of particular tenets of particular schools of Marxism; and the "defeat of Marxism", as a paradigm.
lp