It is about about who is in charge.
Who is in control.
When you fight, it is usually about either you or your partner trying to control a part of each other's lives.
It can be an opinion, an action, a belief, a core life choice, a priority, an attitude, etc.
If you are the one wanting to control an aspect of your partner's life, the way to bring back harmony is to drop it. Let go!
If you are the one defending yourself, the way to bring back harmony is to force your partner in respecting your space, choice or actions.
Enjoy!