David's enemies, who were they?

I came across this verse while browsing through the book of Psalms one morning,

Psalm 18:41
They cry for help,
 - - - but no one saves them;
They call to YHWH
 - - - but He does not answer"

In this verse, David was describing the fate of his enemies, against whom David had been "armed with strength for battle" by YHWH  and over whom David triumphed. (see 18:39-42 GNT), below:

39 You give me strength for the battle
    and victory over my enemies.
40 You make my enemies run from me;
    I destroy those who hate me.
41 They cry for help, but no one saves them;
    they call to YHWH, but he does not answer.
42 I crush them, so that they become like dust
    which the wind blows away.
I trample on them like mud in the streets.

The verse left me wondering who those enemies were. What kind of enemy did David have back then who would call on the Name of YHWH?

I am still trying to ascertain this.