Failure to sign a peace treaty following war
Persistence of hostilities following cease-fire agreements
An armistice does not necessarily put an end to the state of war, especially if the parties fail to make arrangements for the time after the cease-fire. Belligerents may continue to blockade, seize goods, [etc] until such time as final peace agreements are made. A serious violation of a cease-fire agreement gives the other party the right to resume hostilities.
A number of countries are still in a technical state of war, even though the wars in question were terminated many years ago. In 1993 this included USA and North Korea following their 1950-53 conflict.