There are many historical documents in the Southern Song Dynasty. In addition to the long ruling time and the importance attached by the central government and rulers to culture, there is another important reason that the occupied area is mainly the southern region.
The level of sinicization in the Yuan Dynasty was much lower than that in the Jin Dynasty, and the ruling time of the two dynasties was similar. But why are there more documents in the Yuan Dynasty than in the Jin Dynasty? The main reason is that a large number of adherents of the Southern Song Dynasty entered the Yuan Dynasty, continued to write anthologies, poems, monuments and records, compiled anthologies and spread them around. Most of the collected works of Yuan Dynasty were written by southerners, but few by northerners, so that when a Japanese scholar visited the school before, he mainly studied the collected works written by a late man in the north, which provided important information for studying the history of the north.
Now, Yuan Zhang Dian, one of the most important historical materials in the Yuan Dynasty, is a collection of government cases compiled by a bookstore in Jiangxi Province, which is specially provided for local literati who want to join the government as civil servants. Northerners will never think of this kind of business, which is definitely the result of a long history of local cultural traditions.
There are also various ways to compile local chronicles. There are Zhenjiang, Siming (Ningbo), Guo Changzhi (Dinghai), Nanhai (Guangzhou), Jinling, Kunshan (Taicang), Wuxi, Yunnan and Jiahe (Jiaxing) in the Yuan Dynasty. Comparatively speaking, only Shandong's Qi Cheng (abridged edition) and Da Tong Yuan Zhi (edited by southerners, but mostly scattered), and an analysis of Tianjin Zhi, compiled by a Jiangxi person, although most areas are local chronicles.
The north is not without documents. For example, Lu Yechu has his own anthology and exegesis, and Quanzhen also prints the aisle classics, which is also a large number of documents. But on the one hand, people who write essays like Lu Ye Chucai have to print them at home (is there one at the end of the original? Yanjing Zhongshu Assistant Minister's Office has been published? ), Quanzhen religion also printed books on its own (it was later burned, and the power gained by politics was too dangerous), and printed books did not become a part of the industry at all. During the Mongolian period, Lu Yechu also suggested that Emperor Taizong set up a classics department in Pingyang, but he didn't print any books. Bookstores in southern Zhejiang and Fujian never gave up their jobs because of the change of regime, but still printed books. Even the official history books of Song, Liao and Jin Dynasties were printed in Jiangxi and Jiangsu and Zhejiang provinces. Jiangxi, Jiangsu, Zhejiang, Fujian and other provinces have specialized bookstores and mature book publishing industry chains. Why don't you say you don't print books? There are not many documents in the south.
In contrast, the ruler is far from it. There are basically no political books and local chronicles (there is a book called Daikin Collection, a thin volume, and a doctoral thesis has been written? ), so many notes in the collection, not bad. Let's take a look at the Liao Dynasty, whose southernmost border only reaches the northern part of Hebei Province. Now, besides inscriptions, epitaphs and murals, what can we study? Relevant documents can only be seen in the Northern Song Dynasty. Because of the lack of historical materials, Liao history has also been compiled into an extremely mysterious state. In contrast, the literature structure of Jin Dynasty is healthy.
Of course, this answer does not mean to belittle the north at all. It's really hard to say which is more important, culture or strength. It's good to manage one at the same time.