From around the 14th century, the regional identities that roughly correspond to the present-day map of Southeast Asia began to crystalise. The Khmer empire crumbled under pressure from emerging Thai city-kingdoms to the west. Ayutthaya (also called Siam; 14th–18th centuries), the strongest of the Thai polities, grew to cover most of modern-day Thailand and part of Myanmar. The Majapahit kingdom (13th–15th centuries) unified Indonesia from Sumatra to New Guinea, effectively controlling the seas. The kingdom of Dai Viet, long antagonised by the Chinese to the north, came into its own under the Later Le dynasty (15th–18th centuries), extending its border south to form a state that resembled present-day Vietnam.