Diplomatic collapse

I've noticed that there tends to be a point in the mid-late game where even a very peaceful game suddenly goes sideways, not just for me but for basically every AI civ. As near as I can figure out, it's because the differing ideologies that each civ selects create enough diplo penalties that things start going sour among different groups, and the legacy DoFs that still exist at that time make things worse.

For instance, I was playing an Emperor game recently, one that was mostly peaceful (except poor Maria got herself conquered by William and Suleiman) up until the civs started picking ideologies. I got there first and picked Freedom, while everyone else has since picked Order or Autocracy. (Always seems to work that way, I guess.) A couple of rounds of denouncements later, and my old DoFs that hadn't expired yet were becoming liabilities, so I started letting them expire. However, they hadn't all wrapped up yet, and now I'm getting denounced myself. I don't think this'll be a problem, but I'm doing pretty well toward either CV or SV, and was hoping to try to ride this out peacefully until the end (which probably won't happen at this point, so I'm going to make the most of it instead).

So my question is, is there a way to keep the diplomatic situation more stable during the ideology phase of the game, or is the game simply designed to fall apart diplomatically around this era?

keep control of congress and propose popular decisions, Projects are allays popular.

Put vote (1 is enogth) in favor of decision you can live with and you believe will pass anyway, to get + with proposing civ.

If you can not get host vote for civ of your choose that will become host with or with out your votes + with that civ. Share int. Concede to help requests. All that will create positive diplo modifiers that will help you to stay friendly with most people.

The game deliberately tries to provoke wars at this point to "keep it interesting".

If you are seriously interested in preventing war (or minimising the impact) you can consider switching to the majority ideology). The addition of your Civ to that faction will make it utterly dominant (hopefully) and some of your new ideology buddies will likely take out the smaller faction, but you won't need to be involved in any material way. (Declaring war and doing nothing can be a good option sometimes).

If going peaceful I generally go order because most other Civs will follow and we can stay friendly, and because it's even with freedom for SV and cultural (especially because a lot of large empires with huge culture pick up order, so the +34% to order Civs is great)

But yeah, ideologies have a major diplomatic impact, enough to start wars.

Denounces don't come from differencing ideologies alone, there must have some other things you have done. If you wish to play the diplomacy game it starts fairly early and you must be prepared to take some sacrifices. When proposing in the WC you need to pick something that doesn't anger anyone, a good choice is world's fair. When the AI proposes something you'd rather not have passed you can always abstain so you don't suffer any diplomatic relations, except when they propose a different ideology(never get that passed).

i prefer some conflict throughout my entire game. peaceful games bore me but if you are going for peace then start offering helps and voting in majority things in the UN elections ect.

Just FYI: the differing ideology penalty is -45 (same ideology bonus is +45). A denouncement, for comparison, is -35. Proposing something popular in congress is +15, giving someone else host is +20. DOF is +35, and befriending the same leaders is +15, while befriending someone's enemies is -15. Warmonger penalties aren't fixed but often start near -30 for civs who really dislike war, and can bottom out near -250.

In short, the ideology penalty is VERY steep. It's intended to shake the diplomacy game up and split the world into blocs. Unfortunately, nearly every AI likes Order.

Its definitely possible to stay out of diplomatic trouble for a long, long time. maybe all game.
Yes, the rest of the world might squabble like children, but if you play your cards right, you can stay out of it the whole time, even with opposing ideology.

Choose Order. You will never be alone.
Keep up with those DoFs! you dont need to let them go. Just keep an eye on it. You should always be able to keep at least 2 or 3 DOF allied, even when they dont like each other a lot.

Dont forget to agree to one or two research agreements, or some other trade arangements. The AI will be a pinch more loyal to you.

Making the right WC proposals and votes also helps.

Liberate cities, especially AI cities, most especially AI cities that will recall to life someone you could have as a friend. This is really crucial for diplomacy wins, as a recalled to life player is easier to get a vote from (in my limited experience anyway).

going with freedom is often a rocky road unless you are really pushing culture AND tourism. as mentioned it gives an automatic -diplo because most Civs will go with order / autocracy. When pushing toursim you may be able to get one or even two weaker civs to flip into freedom, but you should expect some dirty looks from the other world leaders.

Best to just build a large enough army and have enough of your own influence/culture that you can pick whichever ideology benefits you best personally (in your own opinion) and not worry about what the rest of the world thinks.

Which civs have influence over them is actually a factor in the AIs decision on what ideology to choose, so if you put effort into influence you won't be alone whichever one you pick.
(In addition to the effect that if your ideology has more torches over them, it causes them unhappiness and in some cases leads to the AI calling a revolution to change to your ideology)