Introduction:
Joab, the son of Zeruiah, was a prominent military commander in the service of King David. Known for his strategic acumen and fierce loyalty to David, Joab's life was marked by a series of complex and often violent actions, including acts of revenge that played a significant role in the political and military landscape of Israel during David's reign.

Background:
Joab was the nephew of King David, being the son of David's sister Zeruiah. He first rose to prominence as a military leader during David's campaign against the Jebusites, capturing Jerusalem and establishing it as the capital of Israel (1 Chronicles 11:6). Joab's position as commander of David's army was solidified through his military successes and his unwavering support for David during times of internal strife.

The Murder of Abner:
One of the most notable acts of revenge by Joab was the murder of Abner, the commander of Saul's army. After the death of Saul, Abner initially supported Ish-bosheth, Saul's son, as king over Israel. However, following a falling out with Ish-bosheth, Abner sought to transfer his allegiance to David, promising to bring the tribes of Israel under David's rule (2 Samuel 3:12-21).

Joab, harboring a personal vendetta against Abner for the death of his brother Asahel during a battle at Gibeon (2 Samuel 2:18-23), deceitfully lured Abner back to Hebron under the pretense of a peaceful meeting. There, Joab killed Abner, avenging his brother's death. David publicly condemned Joab's actions, stating, "I and my kingdom are forever guiltless before the LORD concerning the blood of Abner son of Ner" (2 Samuel 3:28).

The Killing of Amasa:
Another significant act of revenge by Joab was the killing of Amasa, whom David had appointed as commander of the army in place of Joab. Amasa, also a relative of David, was tasked with assembling the men of Judah to quell the rebellion led by Sheba son of Bichri (2 Samuel 20:4-5). When Amasa delayed in fulfilling his duty, Joab took matters into his own hands.

Meeting Amasa at Gibeon, Joab greeted him with a deceptive gesture of friendship, only to strike him down with a sword. This act of treachery allowed Joab to reclaim his position as commander of the army (2 Samuel 20:8-10). Joab's actions, while securing his military authority, further demonstrated his willingness to use violence to achieve his ends.

Joab's Role in Absalom's Rebellion:
Joab's complex relationship with David is further illustrated during the rebellion of Absalom, David's son. Despite David's explicit command to deal gently with Absalom, Joab took it upon himself to kill Absalom after he became entangled in a tree during the battle in the forest of Ephraim (2 Samuel 18:9-15). Joab's decision to kill Absalom, though politically expedient, was a direct defiance of David's wishes and highlighted Joab's pragmatic approach to leadership and loyalty.

Legacy:
Joab's acts of revenge, while often brutal, were driven by a combination of personal vendettas, political calculations, and a desire to maintain stability within the kingdom. His actions, though effective in the short term, ultimately contributed to his downfall. In the final days of David's reign, Joab supported Adonijah's claim to the throne over Solomon, leading to his execution on the orders of King Solomon (1 Kings 2:28-34).

Joab's life and actions serve as a complex narrative of loyalty, ambition, and the consequences of revenge within the biblical history of Israel. His account is a testament to the intricate interplay of personal motives and divine providence in the unfolding of God's plan for His people.