The folks at The Warlords have posted an overview of the game's important Brotherhood and Sisterhood system.

Brotherhood & Sisterhood is another unique feature of The Warlords. In ancient China, the brotherhood was everything, and this is what makes up the soul of the Warlords. In the game, three players can be sworn brothers or sisters. After that, they will share Kung Fu and their enemy list. When encountering emergencies, brothers or sisters can instantly be called to come to the rescue.

This was a custom most famously romanticized in the historical novel "Romance of the Three Kingdoms". In the novel, in one of the most famous sections titled, "Oath of the Peach Garden" three warriors Liu Bei, Guan Yu and Zhang Fei became sworn brothers in a special ceremony amongst blossoming peach trees. As it is said, in 188 AD, in the county of Zhuo, the three met by chance and soon discovered they all shared a common desire to serve the country in the chaotic times. The next day they swore their oaths as brothers where Liu Bei was ranked the eldest, Guan Yu the second, and Zhang Fei the youngest. Combining their forces allowed them to quickly muster up more than 300 local men, forged weapons, acquire horses, and joined in the fight to repel the rebelling Yellow Turbans.

Read more here.