The press release provides the context,
“In the north, the tyrant Dong Zhuo has fallen to the blade of his adopted son, Lü Bu: a fierce warrior hellbent on defeating the great heroes of China. In the south, Sun Ce mourns the death of his father, the noble Sun Jian, and pledges his life to continue his father's legacy. The day has come where they must stand alone, the future theirs to take...”
The expansion takes place in 194 CE, a time in which rebellions have been thwarted but discontent and turmoil remain at large. A World Betrayed also ushers in the next update for all Three Kingdoms players. Patch 1.5.0 grants access to a brand-new warlord in the form of Yan Baihu, unique commanders, powerful warriors and eminent statesmen, as well as revamps to the spies and bandit factions, plus much more. Additional details on the accompanying patch can be found here.