As Moroni prepares to move against Lamanite positions, he is surprised by a Lamanite move against Nephihah. We have seen Nephihah as a potential target from the western front, and have noted that it appears to lie on the east side of the Sidon valley between the seashore cities and Manti. Verse 6 tells us that when the Lamanites fled from the Nephite occupied Manti, they traveled down the Sidon valley. At some point they met up with other Lamanite forces, and then planned to take Nephihah. This would be a very important city to hold as it protected the lower end of the Sidon valley. With Nephihah in Lamanite possession, the Nephite armies were essentially split with a Lamanite stronghold between them.