2 Samuel 5:1-10; 1 Chronicles 11-12
David officially became king of Israel at Hebron following the death of King Saul. David was 30 when he became king and reigned for 40 years. He ruled from Hebron for 7 years and six months and spent the remainder of his rule based in Jerusalem.
King David and his men marched to Jerusalem and attacked the Jebusites who still controlled the city. Despite the Jebusites telling David and his men there was no chance of defeating them, David and his men captured the fortress of Zion. David took up residence in Jerusalem and began to build up the area around the city. He became powerful because God was with him.
The first part of 1 Chronicles 11 mirrors the events described in 2 Samuel 5:1-10. The remainder of 1 Chronicles 11 and the entirety of 1 Chronicles 12 lists and describes the mighty warriors of David who began joining him while he was at Ziklag running from Saul and who continued to come to the side of David while he ruled from Hebron. It was no wonder David was so successful in warfare given he had experienced fighting men at his side and more importantly, God was with him.