Old disagreements, old betrayals, old conflicts stretching thousands of years. Most of the stories we were told were about betrayal and how we should not trust them, but I think most stories are only one side, and not the full truth. And stories change in time.
When the dragon Smaug attacked Erebor, our mountain-home, the elves turned away and did not help. Thorin was there, and he blames all of them for the suffering of our kin.