The Maqil Arab warrior tribes who moved south into the western Sahara from the 13th century, imposed themselves on the Sanhaja Berbers, and made Hassaniya Arabic the language of the desert from the Draa to the Senegal. Their victory in the Char Bouba war (1644–74) fixed the social order of the whole region: Arab warrior (hassan) tribes on top, Berber clerical (zawaya) tribes beneath them, then tributaries and slaves — a society whose emirates (Trarza, Brakna, Tagant, Adrar) are the political units the atlas draws separately. This record is the umbrella over that society and the tribes outside the emirates, including the far-ranging Reguibat of the north.
Not an ending: Coppolani's 'peaceful penetration' subdued Trarza, Brakna and Tagant by 1904, and Gouraud's conquest of the Adrar completed French control by 1912, though Reguibat raiding continued until 1934. The Hassaniya-speaking Bidan remain the dominant society of Mauritania and Western Sahara, and the hassan/zawaya/haratin hierarchy this record describes is still the central fact of Mauritanian politics.
The atlas holds 2 border frames for Beni Hassan (Hassani Arab tribes of the western Sahara) — the shape you scrub through changes in 1250 · 1675.
The dedicated study of exactly this event — the Maqil/Beni Hassan advance into the Sanhaja west and the making of Hassaniya society; used instead of a general Mauritania survey.