The estimated time of separation between Ryukyuan and mainland Japanese is a matter of debate due to methodological problems; older estimates (1959–2009) varied between 300 BCE and 700 CE, while novel (2009–2011) around 2nd century BCE to 100 CE, which has a lack of correlation with archeology and new chronology according to which Yayoi period started around 950 BCE, or the proposed spread of the Proto-Ryukyuan speakers to the islands in the 10–12th century from Kyushu. Based on linguistic differences, they separated at least before the 7th century, before or around Kofun period (c. 250–538), while mainland Proto-Ryukyuan was in contact with Early Middle Japanese until 13th century. The Northern Ryukyuan does not, while Southern Ryukyuan does show north-to-south expansion and thus exist several scenarios. It is generally considered that the likely homeland of Japonic and Proto-Ryukyuan expansion was in Kyushu, compared to another hypothesis of expansion from Ryukyu to mainland Japan. As the Japanese (or Yamato people) learned to write and read a thousand years before the Ryukyuans and absorbed many Chinese language forms, the early literature which records the language of the Old Japanese imperial court show archaisms which are closer to Okinawan dialects. The Ryukyuan language is divided into two main groups, Northern Ryukyuan languages and Southern Ryukyuan languages, and generally are considered the existence of five Ryukyuan languages; Amami, Okinawa, Miyako, Yaeyama and Yonaguni, while the sixth Kunigami is added due to diversity. Within them and on specific islands exist local dialects, of which many vanished. Despite the use of Shuri Okinawan in the Shuri Court and its reputation, there's no standard variety. Thus, the Ryukyuan languages constitute a cluster of local dialects termed as unroofed abstand languages, "unroofed" meaning without written standard. During the Meiji and post-Meiji period the languages were identified as dialects of Japanese, and viewed negatively were suppressed by the Japanese government which forced assimilation and standard Japanese language. From 1907, the children were prohibited to speak Ryukyuan languages in school, and since the mid-1930s there existed dialect cards, a system of punishment for the students who spoke in a non-standard language. Speaking a Ryukyuan language was deemed an unpatriotic act, by 1939 a speaker was denied service and employment in government offices, while by the Battle of Okinawa in 1945 the military was commanded to consider Ryukyuan speakers as spies (death penalty) with many reports that such action was carried out.