The presence of this originally insular Celtic population on the Continent is accounted for by their migrations from the British Isles that took place between the third and fifth centuries A.D. , apparently set off by the military and territorial pressures exerted by advancing groups of Angles and Saxons. Their settlement in Brittany was permanent, and Bretons managed for a time (ninth-tenth centuries) to create an independent state, but they were subsequently besieged by both Frankish (the future French) and Norman invaders, which reduced the amount of territory under their control. In 1488 Breton forces were definitively defeated in battle by the French, and in 1532 Brittany was officially annexed to the French state. However, throughout the ancien régime, Brittany retained its own parliament and administrative autonomy. Because of these facts and the sheer physical distance of Brittany from Paris, the Breton "province" was able to retain its distinctive Celtic culture and language, particularly in nonurban areas, which meant most of the vast inland territories of the province. The majority of the Breton people did not assimilate linguistically and culturally into the French nation until the nineteenth century, with the imposition of the military draft and obligatory public education, the creation of a network of highways and railways, and the development of industry. World War I greatly accelerated the assimilation process through the patriotic rallying of the populace and through the disproportionate loss of lives to the war effort (12 percent of Bretons were killed in World War I, though they represented only 6.5 percent of the total French population at that time). The interwar years saw the development of a significant movement for Breton autonomy; for some Bretons this meant also a return to the Breton language and traditional cultural values that they felt had been seriously threatened, if not destroyed, by the French. The movement for political autonomy from France is not so strong today, but there continues to be significant agitation among the people for the development of higher levels of cultural, linguistic, and economic self-determination.
Most Bretons perceive themselves as constituting a distinct ethnic or cultural group within France, at least historically. Divisions within the Breton population are chiefly along class and political lines, though tensions at times are manifested between Bretons and non-Breton immigrant groups in urban areas. Many Bretons also identify with the wider Celtic community; cultural and intellectual exchanges between Brittany and Wales, Ireland, and Scotland have been occurring for a very long time.