Your definition of intact is much different from mine? Thedas is a warring collection of dissident states always at each others' throats with constant in-fighting. Tevinter and the Qunari are only not able to conquer the rest of it due to the fact the fact
The last they time tried, they were facing barbarian tribes or an enemy that outnumbered then five hundred to one?
Tevinter assumed dominion over Thedas when there was little to no organized resistance to meet them, no nation existed save their own and the elven state.
On the other hand, the Qunar faced individual Nations, ones that could throw armies at their problem again and again, and they did, and the Qunari broke under sheer numeric superiority and a few nifty stratagems.
The War bankrupted Thedas and broke, but the Qunari retreated.
Civilization has come to Thedas, such as it is.
Tevinter would no longer face barbarian tribes who spread across what would be a country, they would face armies.
And the Qunari? They lost before because they cannot compete with Thedosian numbers, Humans outnumber Qunari to a ridiculous extent.