List of wars extended by diplomatic irregularity
There are different claims of wars extended by diplomatic irregularity which involve long peaceful periods after the end of hostilities where, for various reasons, the belligerents could be considered to be in a technical state of war. For example, occasionally small countries named in a declaration of war would accidentally be omitted from a peace treaty ending the wider conflict.
Source: Wikipedia — List of wars extended by diplomatic irregularity (CC BY-SA 4.0)