With Saul dead, civil war breaks out. David is from the tribe of Judah, and Judah declares him king. The other tribes of Israel are loyal to one of Saul’s sons. David doesn’t recognize Ish-bosheth as king because God did not appoint him.
David was willing to fight to gain the outcome God had determined. Following God sometimes requires waiting, but sometimes requires action. Over and over we see David seeking God’s direction so he would know when it was time to act. We need to seek God today too.