Albert Barnes Commentary 2 Samuel 3:6

"And it came to pass, while there was war between the house of Saul and the house of David, that Abner made himself strong in the house of Saul." — 2 Samuel 3:6 (ASV)

Translate as: And it came to pass, while the war between the house of Saul and the house of David lasted, that Abner assisted the house of Saul.