i have always thought that market and grocer come into the game way too late, this encourages cottage spamming. However a new building could come into the game almost right away to help with the early economy allowing a player to expand at a greater rate without cottage spamming.
I propose a new building
Slave Plantation
Requirements - Mining,Fishing,The Wheel,Agriculture,and Hunting
Bonuses - +5 trade routes,or just +5 gold, or even take that down a notch or two.
Side Effects - +25% rebel culture, or +1 unhappy person, something like this.
Slavery has existed in almost every time frame in almost every culture, so this would fit in with any civ. It has also not been looked upon kindly for very long by any civ, making the need for the side effects, which would also decrease the advantages of the bonuses, which may be high, but i think it should be right around there. The requirements for this building seem right to me, being the fact that these are all worker techs, and once most of them are researched that should be about time for using of slavery.
This building could also somehow be tied into the slavery civic, or kept seperate as i have proposed it here.
This building should also go obsolete at some point even though it is not a wonder. Say around the modern era, or maybe with constitution or democracy, etc, maybe period 4(don't know which one that is)
This might help with the whole cottage spamming thing or increase the need for it. But it will also help implament your civil war idea.