Country, region, and city used to be three independent filters, which made it easy to construct a search that could never match anything — a German region combined with a French country — and get zero results with no explanation.
Geographic filters are now hierarchical. Picking a country narrows the regions on offer; picking a region narrows the cities. Contradictory combinations cannot be built.
Your selections are also reflected in the URL, so a search you spent time constructing can be bookmarked or sent to a colleague and reopens exactly as you left it.