The concept of Nusantara as a unified region was not invented by Gajah Mada in 1336. Earlier in 1275, the term "Cakravala Mandala Dvipantara" is used to describe the Southeast Asian archipelago by Kertanegara of Singhasari. Dvipantara is a Sanskrit word for the "islands in between", making it a synonym to Nusantara as both "dvipa" and "nusa" mean "island". Kertanegara envisioned the union of Southeast Asian maritime kingdoms and polities under Singhasari as a bulwark against the rise of the expansionist Mongol Yuan dynasty in mainland China.