the path to happiness

150 turns on standard gamespeed?
You can check the public opinion via culture overview -> influence by player
(an example in this screenshot I found: http://cloud.steampowered.com/ugc/576742747479967360/8E3B7F19A4A2821B77EEABE48CED582561598EB3/)

To reduce influence from other players (and unhappiness) you need more tourism. Different than the culture victory, which puts tourism vs culture!
In the example you can see that Poland receives -31 happiness because its tourism is only 85 compared to 348 (autocracy) and 193 (order).

Yup. 150 turns on standard. And I was leading culturally, and no ideologies had been chosen yet.

I will have to check what my tourism was, if I still have that game. I might have saved it, but am not sure.

Usually I don't have problem with having more tourism and leading in that, but then again I only play on Prince.

This game just could have been one of those things. I normally don't get three cities by turn 100. I was worried the AI would forward settle on me and there was a ton of salt I didn't want them to get.

In hindsight--the AI never settled anywhere near me during those 150 turns, which is pretty rare in my experience.