Rather than getting caught up in the who, what and why of each battle, look at fighting as a learning experience for your preschooler.
Disagreements are a part of life.
Just like walking and talking, solving conflict is something every child must learn to do. Yet, unlike physical skills that only require physical readiness, solving conflict calls for a clear sense of right and wrong. But every squabble brings an opportunity to help children discover that there are more objective standards of appropriate and inappropriate behavior. Young children don't have the self-control to refrain from fighting or the ability to settle disputes on their own. They need simple, specific guidelines for working out their arguments.