Final answer:
Srivijaya, Majapahit, and the states on the northeast coast of Sumatra were the principle powerhouses of the 12th century in Southeast Asia. They controlled trade and had significant influence in the region.
Step-by-step explanation:
The principle powerhouses of the 12th century in Southeast Asia were Srivijaya, Majapahit, and the states on the northeast coast of Sumatra. Srivijaya controlled trade between the Indian Ocean and China but was later weakened by the Cholas. Majapahit, based in Java, dominated the region and had states paying tribute to them from areas including Malaysia and the Philippines. The states on the northeast coast of Sumatra, such as Perlak and Aru, followed by Pasai and Malacca, were important maritime centers.