The Dörben Oirad ('Four Oirat'), a confederation of western Mongol tribes (Choros, Dörbet, Torghut, Khoid/Khoshut) of the Altai and Dzungaria; long-time rival of the eastern Chinggisid Mongols, peaked under Esen Taishi — who captured the Ming emperor in 1449 — and fragmented in the 1630s into the Dzungar, Khoshut and Kalmyk khanates.
Broke apart c. 1630-1634: the Choros formed the Dzungar Khanate, the Khoshut under Güshi Khan moved to Kokonor and Tibet (1636), and the Torghut migrated west to the Volga to found the Kalmyk Khanate.
The atlas holds 2 border frames for Four Oirat Confederation (Dörben Oirad) — the shape you scrub through changes in 1399 · 1455.
The standard English scholarly account of the Oirats/Zunghars and their fragmentation into the Dzungar, Khoshut and Kalmyk states from the confederation.