Long before the twelfth Century, Chinese transport had become capable of far voyages, and Chinese merchants sailed straight to the many producing centers in the archipelago. The eastern Javanese ports became more prosperous than ever before. A bigger entrepô, t trade has developed on the coast of Sumatra and Borneo and in the offshore islands in the southern entrance to the Strait of Malacca. Piles of Chinese ceramics from the twelfth to the fourteenth century attest to the occurrence of a significant trading centre in Kota Cina, near present day Medan on the northeast shore of Sumatra.
As a consequence of those changes in the trade pattern, the Minangkabau princes from inner districts of central Sumatra, heir to the pretensions of the great overlords of Srivijaya The Empire of Kertanagara Palembang, were not able to develop their port of Jambi as a wealthy and strong mercantile centre. A vacuum of power thus opened up in the seas of western Indonesia and the Javanese kings aspired to fill it. Java had probably for ages been considered as the center of a brilliant culture, and Old Javanese became the language of the inscriptions of the island of Bali from the 11th century.
The grafting of Tantric ritual on a megalithic shrine in Bongkisam in Sarawak, sometime following the ninth century, is revealing of the Javanese cultural dissemination into the maritime fringes of Indonesia. Javanese cultural sway in other islands almost definitely preceded political domination. Split into the Malay world as well as the cultural celebrity of Java aren’t enough to explain why the Javanese king Kertanagara chose to impose his authority on Malayu in southern Sumatra in 1275. It’s been suggested that the king’s concern was to defend the archipelago from the threat of the Mongol ruler Kublai Khan by coordinating a religious alliance.
But Kertanagara probably also imposed his political authority as well, though his requirements would have been restricted to expressions of homage and tribute. The king’s actions overseas were almost definitely meant to strengthen its prestige in Java itself, at which he was never free of enemies. His political motives are reflected in the Sanskrit inscription of 1289, attached to a picture of the king in the guise of an angry Akdobhia Buddha, asserting that he’d restored unity to Java, his overseas exploits aren’t mentioned. The precise doctrinal content of the Tantric cult of Kertanagara are unknown. In his life time and after his passing, his fans admired him as a Shiva Buddha. They believed that he’d tapped within himself demonic powers that enabled him to destroy the demons that sought to split Java. The fourteenth century poet Prapancha, writer of Nagarakertagama and a worshiper of Kertanagara, on one occasion referred to the king as Vairocana Buddha, and associated him with a ritual consort who was, however, the consort of Aksobhya Buddha. Prapancha also admired the king’s scholarly zeal and notably his assiduous operation of religious exercises to the good of humanity.