Civ is not a wargame. Some people approach it as a wargame and it wound up being one in prior versions, but it was never intended to be that way.
Actually, it was originally intended that way. It evolved into more of a management game as time went on, but Civ 1 was essentially a wargame. The original game had more units than buildings (albeit only by 1 or 2), and micromanagement was very limited - it was the later incarnations that fleshed out the non-combat game. Even so - and coming from Civ IV fans many of whom originally complained about earlier versions of Civ V being a wargame - I've seen comments on the Civ IV forum, the game that departed most from the original in terms of the extent to which it permitted peaceful gameplay - I've seen Civ V described as being better for peaceful play and Civ IV for warmongers.
AIs will still DOW you if the situation is right, but there are many other elements to the game and constant warring is not what the game is supposed to be about.
Constant warring, no - however even though the name was coined for the even more combat-focused Master of Orion, two of the xs in 4x (eXterminate and eXpand) entail aggression. You should not be able to play wholly peaceful games - it's one of a number of areas where, while BNW improved the game mechanically, Civ V was closer to the optimum balance (peace vs. war, tall vs. wide) in G&K, and BNW generally went too far in the other direction.
AIs are more likely to taunt / tempt you into DOWing them now, which is probably more realistic and certainly allows for more player choice about how to pursue victory, or even just playing and developing their civilizations.
The denunciation system is - or at least was - great, but in BNW AI leaders just don't seem to care if someone else has denounced you, so why should you? In G&K and vanilla denunciation could be fatal if not properly managed - it would lead to chains of denunciations from people who liked you less than the denouncer, and eventually someone would go to war. Now if Elizabeth denounces me, it's a case of "that's nice dear, now go away and let me carry on with my turn".
It's an unfortunate case of Firaxis pandering too much; rather than just listening to and evaluating fan criticism on its own merits, they just write out or marginalise systems that fans moan loudest about. They did the same with the XCOM expansion. Panic is a key part of the game, both in its original and new forms, but players were complaining vocally about it so in the expansion Firaxis added a whole slew of effects that meant that, past the very early game, no one was ever going to panic again.