A time of transition, especially between those who had ruled and those who are about to rule, is at best a time of anxiety and at worse a time of incredible bloodshed.
History of mankind is littered with blood during times of transition from one government to another.
There are winners and losers. After some time, David asks the Lord if he should go to one of the Judean towns. God tells him to go to Hebron, and there David is crowned King of Judah. In the meantime, Abner, commander of Saul's army, takes the last remaining son of Saul, Ish-Bosheth, and makes him King over Israel. Thus, it is to be war between the house of David and the house of Saul over the throne of Israel.