Fighting is an inevitable aspect of a long relationship. It usually begins when the couple feels comfortable enough with each other to share their real feelings and who they really are. Early on in the relationship, they may have kept any irritations to themselves from fear of pushing the other away.
After the two feel secure in the relationship, they begin to vent what they held inside or maybe even didn't feel before. Their significant can become a scapegoat for their frustrations, like you would do with a sibling, and now what could have been healthy communication has turned into a childish tantrum. They may forget that their arguments really had nothing to do with each other but originated from outside stress and think that the relationship is in peril. If the two parties keep looking outside or to each other for resolution, it will never happen. Both have to observe their negative emotions as they rise and prioritize them.
For example, you just got home from a long day of work. Your boss has been on you about a project you are behind on. Traffic was bad and you were cut off several times on your way back. When you say hello to your spouse, they forget to ask you how your day was. Normally that wouldn't bother you because there isn't much to talk about anyways, but today was bad and you wanted them to care more so you start an argument. Think about it; was it your spouse that created your anger or did that one little irritation provoked you to take out an entire bad day's worth of frustration on them?
Observing your true motivation in an argument is one big way to help them subside. If you detach from your heated emotions and into a clear state of thinking, you may find that you were initiator of the argument and that your partner was just reacting to your negative energy. This is where solving the problem becomes hard. Your emotions have been going on and on trying to prove a point that you now, thinking more clearly, find ridiculous. You have no choice but to admit this to yourself which is hard enough. To stop this argument you now have to admit it to your partner, but your body is still telling you to stand your ground.
If you can successfully overcome this and apologize, know you have just made a major accomplishment. The more you can overcome your urge to defend the easier it becomes. But beware; this can become tricky when your spouse wants to continue the fight. When you attempt to apologize and instead of thanking you they reply with something like, "Well then why did this all start in the first place?" you are going to feel offended and want to defend yourself again rather than let it go. It is hard to admit something you don't really have to and receive no appreciation for it, but remember that you are really doing it for yourself. When you argue with the person you love, it hurts and you get angry at yourself after the fact. The whole process is a suffering that, with practice, can be transformed into healthy communication.
Your other half may not be able to use these techniques as you can but you can set an example that over time they can't help but follow. Remember that they were only feeding of the anger you presented to them and they are still rolling with it, but if you stay calm and mature about it they will have nothing to go on for very long. The most important thing to do is remain strong, don't be overwhelmed by a sea of emotion, admit when you have created a problem, and try to stay centered if your attempts to do not work right away. Their will be success and many more happy times in your memories if you can master these techniques and I hope they help bring more balance to your relationship.