So Tinfoil Hat Theory time.
King Calenhad traveled to the kossith homeland after abdicating his throne.
Either it was in exchange for help from the Witch of the Wilds, or it was in search of his old friend, Aldenon. I've complained before about how the Qunari's knowledge and version of Calenhad's story makes zero sense.
Calenhad is crowned king in 5:42 Exalted. He is thirty years old. An unspecified time later, there's a bunch of love potion, seduction, and dueling shenanigans, and Calenhad abdicates to his son Weylan I to prevent civil war.
The Qunari land in Par Vollen in 6:30 Steel, and invade the mainland in 6:32.
How did the Qunari know the ideal spot to attack? Par Vollen is lightly held by Tevinter, to the point that two years with not notification isn't even a blip in their radar. It's jungle territory, but the natives adapt to Qunari rule quickly. And it lets them have a secure base, since it's not like any other nation has dreadnoughts.
I figure that, starting a family tradition, Calenhad traveled to the east by boat and encountered the Qunari. They interrogated him, as they tend to do, and he gave them the basic information on Thedas. This information is kept top secret for decades by the leadership of the Qunari, until at last the kossith's pressure grows too strong, and the leadership reveals that Koslun had totally written up on a Promised Land where they could spread the Qun away from the scary-ass kossith empires.
Cue the mass exodus of Qunari and invasion of Par Vollen.
We used to think the Qunari had back-up coming, which was scary.
But the idea they fled the kossith reminds me of that glorious moment in the Codex Alera series.
The race of giant, blood-magic wolf-men have invaded the Alerans' continent in numbers never before seen. But the moment that's scariest for the main character is when he sees that they've brought women and children. And they're burning their ships.
Across the seas, something has driven the Canim/Qunari here. The complete conquest and annihilation of our entire civilization is seen as less dangerous.
EDIT: Liz, I'm pretty sure the Abyss being there and the darkspawn being present is, as you say, a good indicator that the Old God is long gone. It also shows how delightfully tactical the Archdemons can be. It's no coincidence that Urthemiel built up a horde in the Korcari Wilds, and invaded the one country completely unprepared for a Blight. He still managed to, um, completely fail, but I got the feeling he was never the militarily minded Old God anyway. The multiple Blights in the North seems to be an attempt at attrition.
I pity the poor Old God that tries to start a Blight in Par Vollen.