More fractitious politics in the German region leave some capacity for more minor German states to remain independent, though going far back enough to prevent national unification fervor leading to their consumption by the usual suspects is a challenge of its own.
For pushing the boundaries of what could a "state" be, there is/was the self-declared
Kingdom of Tavolara on the titular isle of Tavolara (just shy of 2 square miles) off the coast of Sardinia; it only became part of Italy due to being willed to the state by its last regent after nearly a century of
de facto independence. With a population of only a few dozen people there's a question as to what sort of economy the country would be able to support, but keeping it independent to the present is only a matter of keeping more independence-minded people in charge. (For a very interesting fellow Italian example, though outside the pre-1900 timeframe, there is the
Principality of Seborga somehow attaining independence.)
