From my own experience on emperor, I've been gifted eight cities pushing my unhappiness up to 48 and by selling/razing unwanted cities, trading luxuries, rush buying courthouses/happiness buildings and allying up with maybe two city states I was able to bring it down to only 15 happiness in 6 turns and 9 in 8 turns before any rioting happened.
I think the official "happiness buffer" procedure is to starve your target city a while. At all events it's a suggestion I've heard. (I never play that way so I wouldn't know anything about it...)
Yes, starving/razing can bring unhappiness under control over time, but you do spend several turns at the critical -10 or worse threshold. That is a lot of wasted hammers and it leaves you very vulnerable to counterattacks due to the combat penalty.
Strategies I can think of:
Keep surplus happiness ready with unconnected luxuries, ungarrisoned units (Military Caste), or toggling/untoggling specialists (Democracy).
Have gold ready to trade for luxuries (with AI's) or rush buy happiness buildings (might sometimes need to Annex a puppet just to do this).
Wait to complete happiness buildings and wonders. (e.g. sometimes I will leave Notre Dame unfinished with one turn remaining, so that I can have it ready as soon as I take an enemy city).
Gifting/selling crappy cities to the AI.
Actually I've found that one of the fastest ways to decrease a population's city isn't through razing/starving (limited to one per turn) but to constantly recapture the city. With the insane amounts of damage that siege weapons can do, I find that in G&K you can often lose a city right after you capture it if you leave any enemy siege units in range. But letting your opponent recapture a city (and then taking it back again) will quickly demolish even the largest cities. In some "Scenarios," there might be benefits or penalties that apply (Into the Renaissance may award you points each time you recapture the city, though less each time since the city becomes smaller; Fall of Rome penalizes you each time you lose a city to the barbarians so capturing/recapturing isn't as helpful).
growth is the engine that powers your entire economy. you do want your science, production, gold, and culture output to rise over time, right? you need to keep your cities growing. Having too much growth is NEVER a bad thing unless its a puppet, and as far as I know, puppets can't even celebrate WLTKD.
I'm pretty sure that puppets do celebrate We Love the King. I've had plenty of games where I only own 2 or 3 real cities and have a huge puppet empire and I get LOTS of We Love the King messages.
Also, to a poster who was asking why the feature is in there - it's a holdover from (or a homage to) prior Civilization games. I miss the throne room though.
