Ether 13:18

wherfore it came to pass that in the first year that Ether dwelt in the cavity of a rock, there was many people which was slain by the sword of those secret combinations fighting against Coriantumr, that they might obtain the kingdom.

So in the first year that Ether lived in the cave, many people were killed by the sword. Those secret groups fought against Coriantumr. They wanted to get the kingdom.

During the first year Ether lived in the cave, thousands of people were killed by the swords of those secret groups fighting against Coriantumr, trying to take his kingdom.