It seems like normally "wars" would pertain to a sequence of conflicts
with more or less well-defined endpoints
Why so? We find, for example, theRoman-Etruscan WarsandThe Wars of the Roses, yet thosewarshad no clearly defined endpoints. There were generally no official peace treaties designating the end of those conflicts - they raged on for a certain period, and were then resolved, for whatever reason.
The simple answer to your question is that since theculture warsorthe browser warsare compromised of numerous points of conflict within a fairly discreet period of time, they are referred to aswars. There is no specific endpoint to the individual conflicts, but they are, at large, confined to a particular era, and in a sense characterize that era, because of their scope, and the public's awareness of them.
So, in such context, the use of wars is used to designated a group of related, well known and important conflicts that occur within a fairly discreet period of time. Although each individual conflict might have no specific endpoint, the era characterizing such conflicts does. The culture wars are still being fought, but at some point in the future, they will end, and humanity will move on to otherwars. Thebrowser warsended some years ago. No clear victor emerged and no peace treaty was signed, but no one is really fighting those battles orwars any more. When exactly didthe browser wars end? Hard to say. But it's clear that today they are over, and we have entered a new period - that ofthe Tablet Wars.
Best Answer
A compound subject can be singular or plural depending on what you mean. Penn and Teller is a magic act. Penn and Teller are the actors. In your context you will have to determine for yourself which is more apt, singular or plural.