I have seen the barbs attack other civ cities... but have never seen a civ go after a barb camp or anything. I remember watching Australia (Marla's map) which was largely undeveloped, and full of barbs. It was too far away to make it practical for me, but I was watching from a remote scouting ship. Egypt and America had scouts and military units on the continent, scouting, but ignored the barbs. However, if the barbs attack cities, they probably also attack other civ ships, and that could eventually raise the civ ship to elite.
However, Last night, I was marshalling foces to invade and take the remaining Zulu cities, and get their coal--since I have none, and the zulus were getting testy again. Suddenly, the city with the coal deposit turned brown. No war, no notification, and it was much too far from any Russian city to be a culture flip. When I finally got a ship close enough to see what was going on, the Russians had landed an expeditionary force and were taking city by city. They never declared war, but some of theeir units were wounded.
This is a strange world. China is being super nice--being half my size, and borders next to mine. But she has 4 huge stacks standing around wishing for something to do. Aztecs are warring Germans, but not on either's soil. just on the colonies. America has half-dozen workers in my land, doing nothing, and gives me the snide "Oh is this your territory? We'll leave then." But they don't. I cant do anything, because they have an MPP with England, the only one who would sell me coal... and my rails arent finished. When the Trans-continental RailRoad is finished, or the trade runs out, whichever happens first, then I can do something. I need to rest a few turns from this last war, first.
Fortunately, I just completed the Universal Suffarage monument.. and will be ready to go to war again.
Maybe I should try the communism thing. I'm just too steeped in anti-communism rhetoric, personally, to want to use it.