The longue durée of Bangladesh history is closely linked to the movement of several frontiers. Agriculture gradually replaced the rainforest to create highly productive economies based on rice cultivation on rich delta soils. States first emerged in the south and west and, over time, also in the east. A moving religious frontier slowly incorporated local religions into larger creeds, notably Buddhism, Hinduism and Islam. And a language frontier pushed many local languages to the margins as a result of the rise of Indo-European languages that, by the tenth century CE, would morph into the Bengali language.