Depends on the war.
In my last game, as the Persians on a large map, I was involved in four wars, being the aggressor in three of them.
In the first war, against the English, I was a Monarchy. No war weariness there.
In the second and third wars, against the Iroquois and the Americans, I was successfully waging wars of aggression as a Democracy. This worked mainly because 1) the game was at Warlord level, 2) I had access to luxury resources all over the world, 3) I had developed temples, cathedrals, marketplaces, etc., 4) the wars were SHORT. I only went after specific cities that were comparatively close to my capital and some distance from theirs. 5), and perhaps most importantly, I made multiple alliances against my opponent early in the war. When you have 5 civs allied against you, you stand little long-term chance of survival, even if the original aggressor brokers a peace treaty.
The fourth war was initiated by the Aztecs. After the Americans had been eliminated, much of their former land was unclaimed. I immediately sent settlers along with a few military units, only to have the Aztecs decide they wanted that land -really bad-. They wiped out 3 of my fledgling distant cities in 1 turn. The French soon piggybacked aboard against me, and I had no choice but to enter a major World War. After a few turns of this, I switched to Communism due to good old war weariness. The war was still ongoing, much to the detriment of France, when I was elected U.N. Secretary-General by the Babylonians and Zulus, the only two civs still on the map that I had never waged war against.
