Airbnb has changed the way we travel and upended the hotel industry, but it has also sparked one of the messiest fights ever between a startup and city government. When Airbnb arrived in New York City in 2009, it began operating in neighborhoods where affordable housing was already in short supply. Angry renters complained, and city officials decided to do something about it. But they find themselves up against an equally determined foe, one with deep pockets and powerful allies.