When I first started paying attention to wine, the differences between old world and new world always confounded me in that the old world (your European countries) always label their wines by place, whereas those pesky new world types generally label everything by grape.
(naturally, with anything, there are exceptions).
Our European pals have centuries of tradition growing the same grapes on the same land and rightfully believe that it's that combination of soil, climate, grape, and production techniques that make their wines special and unique. So much that they have put laws and regulations in place to standardize everything.
Part of it is to protect the consumer. The consumer, when they see that name of the appellation on the label, can assume that the wine will have the standards and traditions of that area. Basically.
For example I was just reading about Alsace, that little corner in France that used to belong to Germany. For a wine to be labeled "Alsace AC" ("AC" we will translate to be "appellation control") there are sorts of regulations to follow.
Most obviously is the land involved. The grapes have to be from within the specified region to have the name on the label.
Then there are regulations on how much you can prune the plants, how large your yields can be, and whether you can machine harvest (with robots) or have to do it by hand. Oh, and there's more.
It's rules. Regulations. Quality control.
In the old world, these regulations are the norm.
In the new world, the regulations seem to be more loosey goosey.
Holy cow! How could I discuss appellations and not mention the lovely word "terroir" (Tair-WAHR). The old world producers believe that terroir is the most important thing for a wine. It's the wine's "sense of place".
The internets describes it best...
"a 'terroir' is a group of vineyards (or even vines) from the same region, belonging to a specific appellation, and sharing the same type of soil, weather conditions, grapes and wine making savoir-faire, which contribute to give its specific personality to the wine."
This is always a fun topic - but also for another day.