It is said that it was during his appointment as mahapatih under queen Tribhuwanatunggadewi that Gajah Mada took his famous oath, Sumpah Palapa. The telling of the oath is described in the Pararaton (Book of Kings), an account on Javanese history that dates from the 15th or 16th century:
“Sira Gajah Mada pepatih amungkubumi tan ayun amukita palapa, sira Gajah Mada : Lamun huwus kalah nusantara Ingsun amukti palapa, lamun kalah ring Gurun, ring Seram, Tanjungpura, ring Haru, ring Pahang, Dompo, ring Bali, Sunda, Palembang, Tumasik, samana ingsun amukti palapa “
"Gajah Mada, the prime minister, said he will not taste any spice. Said Gajah Mada : If Nusantara (Nusantara= Nusa antara= external territories) are lost, I will not taste "palapa" ("fruits and or spices"). I will not if the domain of Gurun, domain of Seram, domain of Tanjungpura, domain of Haru, Pahang, Dompo, domain of Bali, Sunda, Palembang, Tumasik, in which case I will never taste any spice."
While often interpreted literally to mean that Gajah Mada would not allow his food to be spiced (palapa is the prose combination of pala apa= any fruits/spices) the oath is sometimes interpreted to mean that Gajah Mada would abstain from all earthly pleasures until he conquered the entire known archipelago for Majapahit.
Even his closest friends were at first doubtful of his oath, but Gajah Mada kept pursuing his dream to unify Nusantara under the glory of Majapahit. Soon he conquered the surrounding territory of Bedahulu (Bali) and Lombok (1343). He then sent the navy westward to attack the remnants of the thallassocrathic kingdom of Sriwijaya in Palembang. There he installed Adityawarman, a Majapahit prince as vassal ruler of the Minangkabau in West Sumatra.
He then conquered the first Islamic sultanate in Southeast Asia, Samudra Pasai, and another state in Svarnadvipa (Sumatra). Gajah Mada also conquered Bintan, Tumasik (Singapore), Melayu (now known as Jambi), and Kalimantan.
At the resignation of the queen, Tribuwanatunggadewi, her son, Hayam Wuruk (ruled 1350–1389) became king. Gajah Mada retained his position as mahapatih under the new king and continued his military campaign by expanding eastward into Logajah, Gurun, Seram, Hutankadali, Sasak, Buton, Banggai, Kunir, Galiyan, Salayar, Sumba, Muar (Saparua), Solor, Bima, Wandan (Banda), Ambon, Timor, and Dompo.
He thus effectively brought the modern Indonesian archipelago under Majapahits's control, which spanned not only the territory of today's Indonesia, but also that of Tumasik (old name of Singapore), the states comprising modern-day Malaysia, Brunei and the southern Philippines.
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