The Union is a loose underground network of thieves and cutthroats which directs its various cells from the main headquarters located in Alent in Libaterra. It started out as a union of small guilds, bandit groups and city gangs which eventually became more and more integrated until the complete loss of Yamato after the Cataclysm made them pull ranks and finally organize into one body.
The Union has spread far throughout the world, operating in various underground cells. Each of the Union's cells in each city names itself, after which they create a city-wide emergency council of one master thief per twenty thieves in the entire city spread equally over the cells. The odd ones out either gain other positions in the local management or possibly take the slack with them somewhere else to start another Cell if the most important outside position is taken or they're deemed unsuitable for it. They recruit people from all walks of life, including assassins, thieves, wizards and bards, and in exchange for the recruits' loyalty they'll protect and take care of them in return.
The most important position in the entirety of city level guild operations is the representative of the city to the main power bases of the leaders, which were formerly based in Steelfall, Etheril, and the remnants of those governments along with the entirety of the Alent headquarters acting in a leadership role. After the losses of Steelfall in a demon raid and Etheril in a Crimson Coalition campaign around 11 AOE, the remaining members of Etheril are planning to relocate to Alent to reorganize themselves and fight against both the Coalition and the demons and grudgingly aid the Grand Alliance in exchange for amnesty for the crimes they've committed.