On the face of it, it would seem that the existence of wars in the Old Testament – in particular wars that God has commanded and approved of – would provide theological support for just war. However, as we examine the narrative of the Old Testament, four critical points arise:
Firstly, the wars of the Conquest were a specific event in God’s salvation plan, and were specifically limited to taking possession of the Promised Land.
Secondly, these wars – and all wars involving Israel – were a function of Israel’s faithfulness; when they were faithful, they won, and when they were unfaithful, they were defeated.
Thirdly, these wars were an out-working of God’s providential sovereignty; God has complete control over all the nations, and Israel’s victories (and losses) came only from his direct action.
Finally, while the leaders of Israel were delegated the responsibility of representing God’s judgement within their own community, the role of judging other nations and those outside of Israel lay solely upon God. In the wars of the Conquest, God commanded Israel to act as his agents, but that was a direct divine command specifically limited to a single circumstance.
War and Judgment
As a result of these observations, we can see that the Old Testament narrative presents war (as Longman puts it) as ‘God’s “strange” work (Is. 28:21) in which he judges evil.’ The people of Israel were given a strong framework for enacting judgment amongst themselves. However, no such framework was provided for enacting judgment on their neighbours. Quite the opposite, Israel was specifically prohibited from engaging in war with neighbours of theirs who were not part of God’s initial command of conquest.
Though the conquest was, in part, an enactment of God’s justice, Israel only took part because God commanded them to. The rest of the history of the Old Testament shows that God enacted his judgment on other nations without any involvement from his people – raising one nation to punish another. This did not make the invading nations’ actions good, or justify the wars that they waged. Rather, God was using the evil actions of people to enact his good purposes.
There is no justification given, either explicitly nor implicitly, for Israel to take part in that work unless they are given a clear prophetic command. While there is no clear command to avoid war, the narrative demonstrates a developing pattern of trusting God’s sovereignty, and leaving the care of the nations to him.
War and Providence
Israel understood God’s providential actions in bringing judgment to the nations. However, this understanding did not result in a theology of Israel participating in this judgment. Instead, the Old Testament reveals a developing theology of leaving the nations to God’s providence, and focusing on individual and national faithfulness.
These observations are not unique. Similar conclusions been advanced by a number of scholars as a result of sustained Old Testament analysis. These conclusions suggest that a faithful reader of the Old Testament, waiting for the Messiah, would not find themselves called to enact God’s justice on the surrounding nations – or even their own occupiers. Instead, the pattern of the Old Testament is to live lives of faithfulness and justice, and trust God’s sovereignty to care for them, judge the nations, and bring about his final justice on the Day of the Lord.
In the book of Genesis, we see clear demonstrations of God’s sovereign power over the world that he created, even while humanity descends into evil. We also see the first expressions of that providential power in his judging of human evil through direct intervention. Finally, Genesis introduces the idea that God can and will enact his providential rule through the evil actions of people.
 Peter C. Craigie, The Problem of War in the Old Testament (Grand Rapids, MI: Eerdmans, 1978), 21–32. T. R. Hobbs, A Time for War: A Study of Warfare in the Old Testament (Old Testament Studies; Wilmington, DE: Michael Glazier, 1989), 14–15.
 Tremper Longman III, ‘Warfare’, in New Dictionary of Biblical Theology (ed. T. Desmond Alexander and Brian S. Rosner; Leicester, England: IVP, 2000), 839.
 Craigie, Problem of War, 93–112.
Lind, Yahweh is a Warrior, 156 ff.
Longman and Reid, God is a Warrior, 47, 60, 71.
Niditch, War in the Hebrew Bible, 134–149.