The animosity against humans was started ever since the Imperium enslaved them, which causes immense trauma that causes anger and hate towards humans. It's called the Domino Effect.
Exactly.
I won't pretend that the Dalish are guiltless. But overall, the moral and ethical weight of condemnation falls more on Orlais and the Chantry than on the Dales.
Okay, so the initial conflict between the Dales and Orlais/Chantry is due to the Dales' isolationism; their religion and culture; and because of eventual border disputes and skirmishes that escalated into war.
What if I were to tell you that the Dales policy of distrust and isolation towards humans can be seen as justified in light of hundreds of years of cultural deprivation, slavery and the fact that their first homeland was utterly destroyed by an aggressive invasion of humans?
Elvhenan was brutally invaded and destroyed by the Tevinter Imperium. Arlathan was sunk into the very ground through powerful blood magic. The survivors were deprived of their identities, culture and way of life and taken into slavery for hundreds of years. A form of slavery where elves were among other atrocities such as forced manual labor, rape, murder and horrific living conditions, sometimes an upward of hundreds of elves were sacrificed to fuel powerful blood magic as seen with the Rifting of the Veil and whatever happened in Kirkwall.
And yes, it's true that Elvehenan was a shell of it's former self by the time the Tevinter got to them thanks to Solas raising the Veil. But that in no way absolves Tevinter of what their actions or of the horrific treatment that they inflicted on the elves. And incidently, elves and humans lived in relative peace for a time until the elves began to fear that human contact was harming them and isolated themselves for self-preservation and warded off later aggressive Tevinter encroachment onto their lands.
So with all of the above in mind, I don't blame the elves of the Dales for being a little more than untrusting of their neighbors in Orlais. The elves wanted to be left alone to practice their beliefs and their culture in peace. Had Orlais and the Chantry backed off from the Dales, it's possible that the Dales would have eventually made diplomatic/economic contact with human nations of their own freewill. However, knowing what Drakon and his successors did to other Rival Andrastianist beliefs and rival faiths aren't exactly indicators that the Dales should expect any less from Orlais or Drakon's chantry.
The fact that a Dalish army was allegedly present at Montsimmond during the Second Blight suggests that the elves may have initially sent help despite their deep-rooted distrust. But halted and turned back when they got a closer look at the situation and the commanders of that army concluded that it was best to withdraw and strengthen their borders rather than die for nothing. Similar to what Thranduil did in the first hobbit movie or what Orlais itself did during the 5th Blight in light of Loghain's prejudice and the Ferelden Civil War as well as during other blights. Furthermore, the tale of Illoren counteracts the idea that the Dalish were completely inactive and helpful during the Blight as Illoren's clan did fight the darkspawn in the Anderfels, far to the north of the Dales.
The Chant also asserts that it wants to spread its dominance and influence across the world, so it's unsurprising that the Chantry-champion/founder Orlais would breath down the Dales' neck. However, it doesn't get to claim the moral high ground just because the Dales wouldn't back down. They also don't get to play victim when the Dales get tired of Orlais' s$%% and go on the offensive after several generations of firm, but non-aggressive restraint. Red Crossing never would've happened if inherent Chantry aggressive beliefs and Orlesian political ambitions didn't pour fuel into the pot.
An earlier poster claims that things wouldn't have escalated if the Dales were willing to compromise. How will compromise work against a party who is inherently unwilling to accept compromise and will settle for nothing less than everything? That would be as ludicrous as the Dwarven Empire trying to make peace with constant darkspawn invasions who've shown no sign of wanting anything accept to destroy and corrupt everything in their path.
Just look what happened after the Exalted March, the Chantry forced the elves to convert and live as second-class citizens in perpetual poverty and misery or live on in constant exile trying to live off the land and evade potential templar pursuit while Orlais took over the Dales. A clear indication that neither the Chantry nor Orlais was ever open to compromise or peaceful co-existence.
In light of all of this, it makes no sense to argue that the fault of the Fall of the Dales falls more on the dalish than any other party when the Dalish just wanted to live their lives in their own homes free from any further human interference or domination. Sadly, the Chantry and Orlais had different plans in mind for the Dales and were clearly unwilling to stop till they got them.