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The book takes time as the axis and systematically combs the course of foreign invasion in the Northeastern frontier in the three hundred years from Shunzhi to Xianfeng. It begins with the situation in the northeastern border in the late Ming and early Qing dynasties, introducing the background and methods of Tsarist Russia's initial penetration into the Northeast; then details the confrontation with Tsarist Russia during the Kangxi period, including the Battle of Yaksa and the signing of the Treaty of Nerchinsk, showing the Qing court's effective management of the border in the early days; and then moves on to Chapter 19 century, it analyzes the whole process of Tsarist Russia taking advantage of the Qing court's internal and external troubles after the Opium War to invade and occupy Northeastern territory through a series of unequal treaties such as the Treaty of Aihun and the Treaty of Beijing. The author pays special attention to the Qing government's decision-making errors in dealing with foreign aggression, such as the ignorance of border officials and poor coordination between the central and local governments. He places the Northeast crisis in the context of global colonial expansion and reveals that the great powers' coveting of China's borders is an inevitable result of the imbalance of the modern international order. The book cites a large number of original historical materials such as diplomatic archives and memorials, and conducts rigorous research to restore the historical truth of the northeastern frontier from relative stability to crisis in three hundred years.