a separate North-Central dialect for Vietnamese as well. The term Haut-Annam refers to dialects spoken from the northern Nghệ An Province to the southern (former) Thừa Thiên Province that preserve archaic features (like consonant clusters and undiphthongized vowels) that have been lost in other modern dialects. The dialect regions differ mostly in their sound systems (see below) but also in vocabulary (including basic vocabulary, non-basic vocabulary, and grammatical words) and grammar. The North-Central and the Central regional varieties, which have a significant number of vocabulary differences, are generally less mutually intelligible to Northern and Southern speakers. There is less internal variation within the Southern region than the other regions because of its relatively late settlement by Vietnamese-speakers (around the end of the 15th century). The North-Central region is particularly conservative since its pronunciation has diverged less from Vietnamese orthography than the other varieties, which tend to merge certain sounds. Along the coastal areas, regional variation has been neutralized to a certain extent, but more mountainous regions preserve more variation. As for sociolinguistic attitudes, the North-Central varieties are often felt to be "peculiar" or "difficult to understand" by speakers of other dialects although their pronunciation fits the written language the most closely; that is typically because of various words in their vocabulary that are unfamiliar to other speakers (see the example vocabulary table below). The large movements of people between North and South since the mid-20th century has resulted in a sizable number of Southern residents speaking in the Northern accent/dialect and, to a greater extent, Northern residents speaking in the Southern accent/dialect. After the Geneva Accords of 1954, which called for the temporary division of the country, about a million northerners (mainly from Hanoi, Haiphong, and the surrounding Red River Delta areas) moved south (mainly to Saigon and heavily to Biên Hòa and Vũng Tàu and the surrounding areas) as part of Operation Passage to Freedom. About 180,000 moved in the reverse direction (Tập kết ra Bắc, literally "go to the North".) After the Fall of Saigon in 1975, Northern and North-Central speakers from the densely-populated Red River Delta and the traditionally-poorer provinces of Nghệ An, Hà Tĩnh, and Quảng Bình have continued to move south to look for better economic opportunities since the new government's New Economic Zones, a program that lasted from 1975 to 1985. The first half of the program (1975–1980) resulted in 1.3 million people sent