the enemies are fairly generally recognized as national enemies.
. . . The situation, then, is that we know who are the enemies in more than 20 psalms. In the other half of all I[ndividual] P[salms] they are described in the same way. From this fact only one method of research can be deduced: we have to suppose, at least as a working hypothesis, that the enemies are of the same kind in those psalms in which their identity is not expressly stated, as in those psalms in which it is expressly stated. 35
Birkeland's point that the enemies in five individual psalms are gentiles must be granted. The texts are quite clear. With the royal psalms likewise the enemies are most reasonably taken to be national (although the Israelite kings did have some problems with "internal security"). The conclusion that all other enemies must be identical because they are described the same way is, however, not warranted. The fact that the psalms were composed and used in the cult means that the enemies must have been, capable of more than one meaning. The reason that descriptions of enemies are the same in all the psalms which mention them is not because the enemies are everywhere identical, but in order that the psalms might not be restricted to a single kind of enemy. If the psalms were to be used in the cult then they had to be capable of referring to more than one kind of enemy.
Birkeland, Evildoers, p. 15.