From the announcement:
The City provides those who live within it a chance to pursue their lives with a modicum of safety and comfort. However, though the outside world is kept outside, any alert adventurer strolling through the City Gate will feel the tension humming in the air. Many different factions are in a constant struggle to dominate the City’s streets. Ultimately, those with the most money wield the most influence, and the three most powerful of these organizations are the Assassins’ Guild, the Thieves’ Guild, and the Merchants’ Guild.
The City expansion includes three new Alternative Ending cards, which reflect the intrigues surrounding powerful and influential guilds. In addition to variant endgames, these card provide global conditions that convey the sway held by these organizations. Going for a glut of gold gathering? Try out the Merchants’ Guild Alternative Ending: