So here's the scenario. I have two rather large and evenly matched empires: one led by human knight sorcerers with bloodline based magic and another by dragons, who are fairly similar to the dragons found in Dungeon and Dragons as far as capabilities are concerned, but aren't colour coded for your convenience in determining their ethics. I want the status quo to be a cold War, with both sides deeply distrustful of each other, but neither keen on the idea of a full blown war.
Here's a little overview of both groups' political and military structures. It's a bit wordy, but I wanted some context for reference.
First, the human knight sorcerers:
The knight sorcerers rule a feudal state with an emperor who grants authority to his vassals down the pyramid of lords and ladies of decreasing importance. So, several local nobles would owe allegiance to a single regional lord. Several regional lords would owe allegiance to the king and those kings would owe allegiance to the emperor.
Law and general government structure is fairly uniform across the empire. While local lords hold a large amount of power, abuse of it tends to end badly for the lord in question. And while not a democracy, all citizens do have some basic rights (no imprisonment without trial and such). Personal freedom has its limits, since all citizens normally belong to a specific lord's domain by birth, but it's an era of licenced movement and loose grips. As long as your paperwork and taxes are in order, things tend to go smoothly.
Local militias are well organised and a centrally controled army serves the emperor directly. Their job is to deal with any situation that's too serious for a local lord and his militia to deal with on their own. Military technology-wise, pikes and crossbows are extremely common. But primitive firearms, cannons and use of fantastical beasts also occur. Cannons are far more common in the regular army, but fantastical beasts such as griffins, wogs and hydras are more frequently used by local militias.
And now the dragons:
The dragons are ruled by a dragon empress and her family. The empress is an absolute ruler, but a fairly pragmatic and wise one. Male dragons each have their own lands and humans that belong to them. They can do what they wish with both, but poor management tends to get them in the empress's bad books. Getting in trouble with the empress tends to result in said dragon's authority and position being taken from him and granted to another dragon who's managed to curry favour through good results and managing things well. Female dragons don't own lands, so instead tend to take a strong interest in subjects other than ruling. They tend to hold positions like alliance brokers, priestesses, spymasters and scientists.
A major reason for this is a male dragon can sire half-dragons and spawn whole lines of dragon-blooded servants, while female dragons can not. These dragon bloods are considered from a legal point of view to be partly the dragon in question whose blood run through their veins. This grants them considerably more rights and privileges than normal humans. But it also means that their actions tend to reflect more the dragons' "favour the Empress" culture. As a result, a strong sense of blood loyalty is found among dragon bloods, knowing that if they do well, it will be their closest relatives that will likely reap the benefits. It is also why most of the dragon empire's high ranking positions are held by dragon- bloods. Dragons are relatively few in number, but trust blood to get things done.
Humans living in dragon lands, by contrast, have no legal rights or protections and their dragon overlords can do what they want with them. Also while it's considered bad form to harm another dragon's humans. It's typically something the offender would fix by paying a fine or doing the aggrieved dragon a favour.
Due to how the dragon empire is structured local law varies greatly, and all armies belong to a specific dragon. Dragons themselves exercise considerable martial might and some are tactical geniuses, with some of the older half-dragons not being far behind. Elite dragon-blood regiments tend to be common among the more martially gifted and older dragons, though the human based part of the armies tends to have poorer training and worse equipment than the knight sorcerers' forces. This is due, in part, to a less centralised and weaker infrastructure. Cannons and other firearms are pretty rare as a result.
What ways might I keep these two empires from trying to start a war with each other?