I would say that we do not use tags to define the scope of a question, but to group questions about similar topics, and to make them easier for enthusiasts to follow. While it makes obvious sense to replace tags with more specific ones as they become available, it doesn't serve anyone to have a thousand tags with one entry in them, either.
One of the problems with a site simply called "history" is that there are many approaches to history. Some have an interest in a time period, others in a particular civilization or cultural group, others in an aspect of human society across time periods and civilizations, others in a particular school of analysis applicable to all of the above. As the site is still in its relative infancy, we lack a complete set of tags for all those angles, (we don't even have angles). Moreover, we are also limited to five tags per question, and there is no way to set up hierarchical relationships between tags.
At the same time, a thousand tags with a single question in each doesn't make it easy to follow questions about the same topic. You subscribed to military but didn't see my question? Well, silly, you should have subscribed to air-force instead. No, wait, to aerial-bombardment. Sorry, I meant strategic-bombing. Well, I wouldn't have tagged it as military, since it's not a question about the entire military, right?.
So, tags like europe are not just for questions encompassing all of Europe, but for questions about topics within Europe that do not [yet] have a more specific tag, so that enthusiasts and experts in European history can have a go at them. Have a question about Henri IV? Great, tag it with france. But a question about the Polish-Lithuanian Commonwealth? For now, I'd say tag it as europe, until we have a half-dozen questions just about the Commonwealth and can justify spitting it out as a specialty.