Having healthy stamina and a good cardiovascular system is good for everyday activities as well as being able to fight.  Without it, you would not last. Sport Karate sparring matches usually take two minutes, while boxing can take two or three minute bouts.  MMA usually has five minute rounds as well.  This does not even include how many rounds these fights go for, which extend the amount of time longer (unless you knock out your opponent in the first round).
Running is an exercise that has been around for centuries and is a proven method to increasing your cardiovascular system.   Personally, I hate it.  When I think about running at 80% intensity for a two mile or three mile run, it is torture.  There is nothing fun about it for me.  I do understand, however, it is important for any good fighter to add into it.  There are creative ways to add running into your regimen that not only is fun, but can get the job done.  Take for instance about parkour.  
Brief Topic on Parkour
What is Parkour?  This type of running sport is also referred to as free running.  You run as fast as you can doing tricks over obstacles, learning different ways to overcome a hurdle, etc.  It looks fun, and in some basic way, it intrigues me to run a variation of it.  It requires a lot of endurance and athletic ability, but is probably worth it.  Not so into the demands of this sport?  Well, I have a workout that will help you as a fighter to increase your endurance.
Running Intervals
Intervals are a great way to get your heart rate up, without having to run long distances.  Interval running is when you run at different speeds, distances, or for variations of time.  For instance, you run as fast as you can for one minute, and walk or jog for thirty seconds.  You can run and burn more energy and fat in less time than running a five mile in one hour.  As you read further, I have posted some ideas on creative running drills to improve your stamina.
Thirty Second Sprints
In this drill, you will run as fast as you can for thirty seconds.  This would be the most basic level of running.  Your goal would be to sprint for thirty seconds, followed by a thirty second rest.  Complete this run so that your time either ends at two, three, or five minutes.  Ten sets would equal five minutes.
Random Intervals, J.W.S.
This drill would require interval running.  Jog for one minute, sprint for one minute, walk for one minute.  Try to complete a two mile run with this interval set.  Knowing that you can take a walk might eliminate the torture of running.  It does for me.
Conclusion
If you are not much of a fan for running, I hope these exercises give you inspiration in adding running exercises.  Some of the best fighters have outstanding cardiovascular endurance.  The better your cardio is, the longer you can last in the ring.