155. Yoink! As Austria, replace another civ as allies with a City-State and acquire the City-State through diplomatic marriage in the same turn.
To get this one, be sure to have enough gold to make the City state your allie from 1000-1500 plus marriage costs other +350. So when you have 2000 wait for other civ to get in alliace with a city state and go for it.
1. Gift gold 1000 or more until is your allie
2. Diplomatic marriage