Dialect continuum

Dialects are all there is: the ‘language’ part is just politics. A dialect continuum is a group of related dialects spoken in a contiguous area. In dialect continua, contrary to the popular notion of languages with sharply defined boundaries, the spoken vernacular changes gradually as one gets geographically further away from a given starting point, with there being no definite point at which one "language" ends and another begins.

Dialect continua and "languages"
With the emergence of the ideology of ethnolinguistic nationalism, according to which a state must have only one official language, the new nation-states began to classify forms of speech within their borders more or less closely related to the official language as being merely "dialects" of it, even when these dialects may have formerly been considered separate languages. Such classifications may also play a part in territorial bickering, as a nation-state may claim dialects not only inside but outside of its own borders as "actually" being dialects of its official language. This is the case, for instance, with many Bulgarians' insistence that Macedonian is a Bulgarian dialect; this is not merely a linguistic claim, but also a political (irredentist) one, in that its purpose is to provide a justification for Macedonia being incorporated into the Bulgarian state. Since, of course, the vernaculars in dialect continua form a gradient and do not have clearly defined boundaries, arguments such as those proferred by Bulgarians and Macedonians are generally political, and have more to do with issues of identity than any actual objective linguistic criteria. While some dialect continua, such as the South Slavic continuum in the Balkans, have become politically fragmented into many "languages", others no less diverse, such as Arabic and Chinese, are considered by their speakers to consist entirely of "dialects" belonging to only a single "language". As linguist Victor Friedman notes:

From the point of view of language as a means of communication, the vast majority of South Slavic dialects form a single continuum from northern Yugoslavia and adjacent parts of neighboring countries all the way into northern Greece and to the Black Sea coast of Bulgaria in the south and east, respectively. At any given point along this continuum speakers can understand speakers from contiguous points. As the distance between points increases, however, so do dialectal differences, albeit not at a steady rate. Isoglosses tend to cluster in some regions and fan out in others. Nonetheless, there does not exist a single location where one can draw a line between mutually unintelligible dialects. The definition of “language” under such circumstances is made on the basis of other criteria, e. g. ethnic or religious self-identification, geographical or political boundaries selected for extra-linguistic reasons as definitive, etc.

Often nation-states, in their attempt to create a linguistically homogeneous population, pursue policies to stamp out dialect continua and unrelated languages and replace them with a standard language, such as in the  in France, in which the French government tried to eradicate Occitan and other forms of Romance languages on the basis that they are merely incorrect forms of French.