Also make sure there are no Carthaginian temples left when you take it... That temple of Baal can totally ruin your day!
As the Julii I was able to take and hold Carthage after my moment of Genocidal madness... I also trained a lot of troops there later and this helped reduce unrest, (Carthage was very well developed when I took it) they then went overseas to rampage in Gaul.
Build Carthage up and train lots of troops there... This will again help to curb unrest and keep the population down a tad.
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