Medieval guilds resorted to solemn initiatory oaths and other elements of secrecy primarily for economic self-protection. Throughout history, revolutionary, subversive, and conspiratorial groups have organized secretly, as in the case of the Sons of Liberty in the American colonies. The repression of liberal, nationalist, and republican movements in Europe in the 19th century, for example, produced an underground network of revolutionary secret societies such as the Italian Carbonari. Other examples may be found in the Irish Fenian society and the Decembrists of imperial Russia.

https://www.britannica.com/topic/secret-society