The "Contention between Niu and Li" refers to the long-term rivalry between the famous politicians and literati of the late Tang Dynasty, Niu Sengru and Li Deyu. This controversy lasted for nearly 40 years and involved multiple political issues, including bureaucratic systems, imperial examination systems, religious beliefs, ethnic issues, etc. It became one of the important events on the political stage of the late Tang Dynasty. The core issue of the "Contention between Niu and Li" lies in the attitudes of both sides towards political reform. Niu Sengru believed that political corruption and unfair bureaucratic systems prevailed at that time, and reform was necessary. He advocated selecting talents through the imperial examination system, implementing a fair bureaucratic system, strengthening supervision of officials, and promoting political clarity. On the other hand, Li Deyu believed that the fundamental cause of political corruption was the decline of moral standards, and it was necessary to strengthen the cultivation and education of scholars, restore the moral ethics of Confucian tradition, and thereby improve the political situation. Additionally, when Li Deyu was in power, he emphasized military affairs, relentlessly suppressing internal rebellions and resisting invasions from the Huihe and Tubo tribes. On the other hand, the Niu faction relentlessly suppressed dissenting officials, leading to the expansion of the scale of the party struggle. Furthermore, Niu Sengru and Li Deyu also differed in their attitudes towards feudal lords. Niu Sengru advocated limiting the power of feudal lords and strengthening supervision over vassal states, while Li Deyu advocated the use of force to suppress vassal states and maintain the authority of the central government. Apart from these focal points of dispute, the "Contention between Niu and Li" also involved the issue of professional critics besieging pragmatists. In the late Tang Dynasty, professional critics flourished, attacking politicians through written articles for fame and profit. These professional critics often lacked firm political stances and attacked others solely for personal gain. In this controversy, professional critics utilized their writing skills to attack their opponents for payment or fame, further deteriorating the political situation. In contrast, figures like Niu Sengru and Li Deyu stuck to their political stances and put their thoughts and political ideologies into practice, contributing to the political stability of the Tang Dynasty despite their disputes. The "Contention between Niu and Li" had profound impacts on the political situation of the late Tang Dynasty. This controversy failed to effectively address the issues of political corruption and unfair bureaucratic systems in the Tang Dynasty, while also weakening the authority of the central government and exacerbating the political crisis. Additionally, the emergence and activities of professional critics further deteriorated the political situation and intensified social unrest in the Tang Dynasty. However, the "Contention between Niu and Li" also reflected the thoughts and efforts of politicians in the late Tang Dynasty towards political reform. The political reform ideas of Niu Sengru and Li Deyu had positive impacts on the political development of later generations. Furthermore, this controversy also demonstrated the difficulties and challenges faced by politicians in the late Tang Dynasty when dealing with political issues, providing valuable lessons for later generations of politicians. In summary, the "Contention between Niu and Li" not only reflects the rivalry between politicians and the rise of professional critics in the late Tang Dynasty, but also reveals issues of political corruption and unfair bureaucratic systems. It provides important historical references for the political development and lessons learned by later generations.

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