Battle of Dale

The dwarves refused to submit to Sauron or help him find the One Ring. So Sauron sent a force of 200,000 Easterlings up to take the Lonely Mountain. Let that sink in for you – More that twice the number of troops were sent to take the Lonely Mountain than was sent against Minas Tirith in the books and 2/3 of the total movie force. That was a huge blunder on Sauron's part. Dale had also been reestablished and like the Lonely Mountain had grown in size and wealth over the years since the Battle of Five Armies. So they were well armed and ready.   Their combined force was 30,000 dwarves and 20,000 men. The men came from Dale while the dwarves had troops from both the Lonely Mountain and the Iron Hills.

The battle started in a field outside Dale. But the Easterlings were too good and numerous. So they pushed the Dwarves and men back to the Lonely Mountain. Then it devolved into a standard siege.

At first they attempted to win in open battle, but that did not go well for the dwarves and Dale troops. They responded by withdrawing into the Lonely Mountain, where the Easterling attack faltered due to the power of the gates. When Mordor’s armies were defeated at Minas Tirith and the destruction of the One Ring saw the morale of the Easterlings collapse. The garrison troops were able to sally forth and drive them back.

Losses were 100,000 Easterlings, 14,000 Dwarves and 12,000 Men from Dale.

The most obvious consequence is the saving of Dale and the Lonely Mountain. The destruction of the One Ring meant that a strategic level Easterling defeat was ultimately inevitable. However, the massacre of the residents and the pillaging of the mountain's wealth could have still occurred of the dwarves/men lost. From there, the forces of Mordor would be perfectly in place to trap Mirkwood in a Pincer. Easterlings could march from the Lonely Mountain and catch the elves between themselves and Mordor's orcs from Dol Guldur. This means the northern reaches of Middle Earth remained free in part because of this defeat for Mordor. Galdalf actually notes that defeat at the Lonely Mountain would be such a devastating blow that victory at Minas Tirith would have been meaningless.