The wide topographical diversity of Southeast Asia has greatly influenced its history. For instance, Mainland Southeast Asia with its continuous but rugged and difficult terrain provided the basis for the early Khmer and Mon civilisations. The sub-region's extensive coastline and major river systems of the Irrawaddy, Salween, Chao Phraya, Mekong and Red River have directed socio-cultural and economic activities towards the Indian Ocean and South China Sea. On the other hand, apart from exceptions such as Borneo and Sumatra, Maritime Southeast Asia is a patchwork of recurring land-sea patterns on widely dispersed islands and archipelagos. A discontinuity that admitted moderately sized thalassocratic states indifferent to territorial ambitions where growth and prosperity was associated with sea trade.