The Battle of Ingdal's Arm was a battle between Indrila's human army and the half-elves that took place in what would become Aglarond in 1065 DR. The battle was won by Brindor's half-elves, and Brindor went on to become king of the newly created nation of Aglarond.
The declining elves of the Yuirwood began interbreeding with the humans who came to explore the area, creating the half-elf population in the area. These half-elves took exception to the humans felling the wood in order to create settlements and inhabit the land. Although the half-elves appealed to the humans to stop this behavior, the warnings were not heeded, and in 1065 DR, the half-elves attacked.
The half-elves descended upon the human population, killing any humans they encountered, and driving them back towards their own coastal cities. The humans in these coastal cities were more vengeful than those inland, and launched a counter-attack from Velprin. This was quashed by the half-elves, and the humans were completely eliminated at Ingdal's Arm.
Most of the surviving humans from nearby settlements were content to make peace with the half-elves, and negotiation ensued, leading to the creation of Aglarond, under the initial rule of King Brindor. Those humans who did not accept the rule of the half-elf king migrated away, to Altumbel or the Fang.