How to end war with Computer nation?

So, I am a relatively new player & I had just conquered my first NPC nation south of me, and my buddy operates west of me, so I have to expand south & east of my corridor. I started a war with the NPC nation directly east of me as it would complete solid empire square. While I thoroughly waited & prepared for my invasion of the southern nation, and blitzkrieg-ed my way into the capital quickly ending the war, knowing my economy could sustain the war for a short while, I figured I could run off the steam & just as quickly move into the last nation standing in my way of having a complete three nation square; and sadly, a failure on my part, I neglected to check the states of the nation to my east, and whoever had it last, built it up OP, but it s currently without a president. It will take more than I am capable of at the moment to take the nation as I lack the weapon, equipment, manpower & economic means. So; I have requested peace with

You will be ok.
Against computer nations if you don't attack for 24/48 hours, war is automatically ended.