Alma 43:14

Now those descendants were as numerous, nearly, as were the Nephites; and thus the Nephites were obliged to contend with their brethren, even unto bloodshed.

There were almost as many of these descendants as there were Nephites. So the Nephites had to fight their own relatives, even if it meant killing them.

These defectors were nearly as numerous as the Nephites themselves. So the Nephites were forced to fight their own relatives to the death.