Is “Flooding the Seven Armies and shaking the realm” true?
attested in history
The Records of the Three Kingdoms, Book of Shu, Biography of Guan Yu records that Guan Yu took advantage of the rising Han River to capture Yu Jin alive and behead Pang De, shaking the realm, and Cao Cao even considered moving the capital.
Guan Yu
In official history, he was a famed general of Shu Han who shook the realm, while in the novel he is portrayed as the peerless warrior and paragon of loyalty, the Saintly Emperor Guan.