What is a opposite example of federalism?”
A non-trivial question! I’m answering this question even though I suspect it is homework. A kingdom is an example of federalism but does not cover all the cases. One might think that “republic” would be but the US is a republic with a federal system whereas France is a republic without a federal system. There does not seem to be one word that describes the opposite. The Wikipedia entry does not provide a name that covers all countries lacking a federaist system but does provide further examples.