Generally it is but not to ridiculous degree of vanilla or some of betas that had bugged, passive AI. And sometimes near constant war cannot be avoided by later eras. I am kinda happy that the mod now introduces some sense and realism into tradition few cities play. You cannot expect to be basically a cultural city-state and be treated by warmongers or even opportunistic progress AIs as anything else as 15 wonders for a cost of taking one city. Wonder-whoring and spamming GP can hardly be called quiet activities. When playing progress you really should have ten or twelve cities to utilize your tree, but then you have more territory, supply, production and gold, so defending yourself should be much more manageable, so I will focus on tradition.
Which strategy do I employ to maintain peaceful relations? Getting bombers and nukes as soon as possible to protect my cities when carpets of land and naval units arrive. They will peace out eventually. In the late game you cannot stay peaceful for long when you approach winning and grabbed one third of all wonders.
Early in the game, strategic placement of secondary cities is the most important thing, they need to guard the way to the capital (which will be producing 80% of your yields). Assessing and then utilizing your territory becomes your primary objective to ensure survival. When warmongers are nearby, and you have little lakes, mountains and jungles to block access to your capital and minimize number of tiles from which your cities could be hit, no wonder is as important as the Great Wall. Use terrain to have as short and as deep front line as it possible and shuffle units. Prioritize ranged units, depending on terrain with logistics or plus one range. You can be fine without the Wall, but it seems that your are having a hard time, so I encourage you to reevaluate it, if you tend to disregard bottom of the tech tree, as many peaceful players do. The same with the Brandenburg Gate for military supply.
When it comes to diplomacy. When you border warmonger, forget it. When you border others try to not piss them off by rivaling for the same city-states. Sending trade routes to them can be helpful, but it is a gamble, as you may lose your trade units in case of DoW. Generally cunning when comes DoFs and denouncements to make your enemies hate each other and war themselves, not trying to maintain good relations with everyone should be the goal. If one possible enemy asks you to go to war with the other, do it. You may gain a temporary friend, instead of having two enemies.
Another thing: If you do not share a border with a warmonger and when his influence is only local (limited to conquering one or two other AIs, though even with global ones you should consider it) and you share some enemies, it is worth aligning with him, even if you nominally play peaceful. Some (not all) warmongers make great friends (it is hard-coded in their flavor, Napoleon or Montezuma do not, Genghis Khan does, just like Shaka and Harald).
Here are flavors from vanilla, they should be largely up to date. Your cooperation should last longer than with the others, as you will probably be warmonger's only friend. And you have to assess how other relations will be affected. Sometimes cooperation with global warmonger is extremely beneficial and even let's you eliminate or neutralize contenders to cultural or scientific victory with his hands. Sometimes, especially if he is loosing against some coalition, it can put you on the same boat of hatred and denouncement and wars as him and sank you even further.
