War was a constant feature in the history of Israel from its beginnings until the destruction of the Second Temple. The nature of the Israelite wars changed according to political and sociological conditions. This can be seen in the differences between the conquest and settlement, the defensive wars of the tribes against their aggressive neighbors in the period of the Judges, the wars of consolidation on the borders during the first days of the Monarchy, the constant struggle for the existence of the Kingdoms of Israel and Judah, and the last desperate stand against the great imperial forces. The days of the Second Temple were marked, too, with long periods of continuous warfare.
In the earlier wars mainly concerned with border disputes, and in the later wars of liberation from imperial control, first Seleucid and then Roman, the principal cause was religious; that is, they were struggles to preserve a national identity based on the Temple in Jerusalem and the Jewish religious laws.
Two types of wars from ancient times can be distinguished: (a) wars of defense and expansion, which were basically political, fought out of physical necessity and to which there were fixed legal limitations; and (b) holy wars, compulsory for the entire nation.
Deuteronomy chapters 20 and 21 contain some of the laws of war which were upheld in the First Temple period, describing the encouragement of the troops by the priests, who assured them of the support of the Lord (Deut 20:1-4). Other sources indicate that the kings and military leaders often consulted oracles for signs of assurance. The priests and holy ark even accompanied the army on the battlefield in the earlier wars (I Sam 4:4; 30:7; II Sam 11:11). Further, to secure God's aid, the troops would offer sacrifices prior to battle (Judg 6:20, 26; 20:26).
The laws concerning war in the Book of Deuteronomy deal, inter alia, with the instances in which persons could be exempt from military service, such as those who were seized with fear, were newly married, had recently built a house, planted a vineyard and so forth. Other laws deal with vanquished peoples, spoils, prisoners and the prohibition of cutting down fruit trees in conquered lands.
The customs and laws of war were fixed and had much in common throughout the ancient Near East. Troops were often drawn from the peasantry, fighting was generally limited to the agricultural off-seasons – from just after harvest till the first rains. Only by keeping a strong army could a nation keep potential enemies at bay, and the only satisfactory alternative to war was to accept all the enemy's demands.
Israelite military inferiority forced the tribes to rely on deception of the enemy; they usually found it too difficult to penetrate fortified cities by force and thus they resorted to other means, such as sending spies into the city to seek out hidden ways (Josh chap. 2). At Ai (Josh chap. 8), the Israelites succeeded in luring the enemy out of the city by a ruse. Later, David captured Jerusalem by secretly penetrating an underground water conduit (II Sam 5:7-8). Night or dawn attacks were also sprung (I Sam 11:11), as well as other forms of surprise attacks (Josh 10:9).
In the period of the settlement, the Israelites had to withstand the attacks of various nomadic tribes especially in the south (the Amalekites) and in the Jezreel Valley (the Midianites), who would raid villages and take prisoners. Warfare against these peoples was conducted by means of small and maneuverable units.
Using these tactics of combined small attacks and opposing the enemy in open array, the Israelites succeeded, at least at first, in standing up to their bitterest rivals, the Philistines.
Upon the death of Saul and his son Jonathan, it became obvious that new tactics were needed. The Philistine threat was the main impetus for the union of the Israelite tribes into a single kingdom since only political unity could bring about a standing well-trained and equipped army.
The army organized by David, under the skilled leadership of Joab, soon gave the Israelites military superiority over the small surrounding states but there was never a day of peace throughout David's reign.
The great victories of the Israelite army in the days of David, and the expansion into most of Syria, can be explained only by the fact that by this time the great empires were no longer able to control his region.
When Israel was divided into two kingdoms they were at first rivals, but later came to conduct combined operations against their common enemies, especially the Arameans who, with their soldiers and weapons, were as strong as the armies of Israel and Judah, and the struggle between them was long-lived. Ahab gathered his troops and ambushed the Arameans while they were still on the march, thoroughly routing them (I Kgs chap. 20). This method of ambushing in narrow mountain passes by large, well-equipped forces, took maximum advantage of the difficulties encountered by anyone attempting to penetrate the hills of Samaria or the Judean mountains; it became one of the standard methods of warfare among the Israelites until the fall of the kingdoms.
The wars fought against the mighty armies of Assyria and Babylonia were different from those waged previously. In the initial clash (in the mid-9th century B.C.), Ahab participated in a league of southern Syrian rulers against Assyria, which repulsed them in four successive campaigns. A hundred years later when the Assyrians attacked, the petty kingdoms were unable to unite, and the war degenerated into mere defensive actions, centered upon fortified cities with the Assyrians in complete control of the countryside.
The main problem in preparing a city to withstand a siege, besides the construction of the fortifications, was to provide for an adequate source of water within the city walls. This was achieved either by digging vast cisterns for storing quantities of rain water, or by diverting water sources beneath the ground to within the fortified area, concealing any original opening outside.
The methods of pressing siege in the ancient Near East were many and varied. Egyptian and Assyrian reliefs show the scaling of walls by means of ladders; breaching walls with battering rams; breaking down gates with axes and fire; and mining beneath walls. Often several methods were employed simultaneously. The Assyrians were depicted as slaying prisoners beneath the very eyes of the besieged so as to weaken their morale.
If a city resisted all these measures, the attackers had to fall back upon the difficult pursuit of an extended siege, cutting off the inhabitants of the city from all supplies, and making continuous attacks upon the walls at various locations until a weak spot was found or the city gave in. After the appearance of the great imperial armies in Palestine, the Israelite kings concentrated their efforts on fortifying and preparing their cities to withstand prolonged sieges. They sometimes succeeded in stemming a siege of many months or even years. There is a depiction of a Judean city under siege by the Assyrian army, in a relief from Nineveh, showing Lachish as the Assyrian troops were storming its walls with many battering rams, light archery in the fore (mostly non-Assyrian troops from vassal kingdoms), then heavy Assyrian spearmen and archers, followed by slingers. The defenders, on their part, attempted to forestall the work of the siege machines by shooting arrows and throwing stones, oil and flaming torches down upon them.
The idea that God himself initiates war (Ex 15:3) and leads Israel in its military campaigns is prevalent throughout the OT (I Sam 18:17; 25:28). Israel cannot be successful in battle without the approval and participation of God. The deity declares war (Ex 17:16; Num 31:2), is consulted by various cultic means prior to battle (I Sam 28:6; 30:7-8; II Sam 5:19, 23; I Kgs 22:5-7), and selects a charismatic military leader to commands his people in warfare (Judg 6:34). Any enemy of Israel is by definition the Lord's enemy. Since the Lord is the strength of Israel, any initiative on the part of secular rulers to participate in war, relying on their own strength and resources is doomed to failure (Is 30:1-5; 31:1, 3; Jer 9:23; Amos 2:13-16). Moreover, it is considered a flagrant violation of the covenant between Israel and God, and is punished by God's employing a foreign nation as his own instrument of war against Israel (Is 10:5-6).
The Lord of Israel also conducts warfare against foreign nations. They are punished for either oppressing Israel (Jer 46:10; Obad vs. 10-14), or for their own pride and major infractions of human conduct (Is 16:6-7; 18:1-5; Jer 49:16; Amos 1:3-2:3).
The prophets, however, foresaw the day when all warfare would cease and in its stead there would reign a universal peace (Is 2:2-4; 11:1-9; Mic 4:3-4).
The NT on the whole is inclined to peace rather than war (see PEACE). This attitude reflects Jesus' personal character as a non-violent sage both in his practice (Luke 9:54-56) and teaching (Matt 5:9; 26:52). On the other hand, he did not forbear to accept a zealot among his followers (Luke 6:15). Jesus' characteristic attitude remains the supremacy of love of God and neighbor (Matt 22:36-40) even to the point of loving enemies (Matt 5:43-48). These different attitudes can be reconciled; for the NT, war is not an ideal (as it was for example in Homeric society). It reflects a lower stage of morality in comparison with love of enemies. But it is sometimes a regrettable necessity until one's opponent has evolved to the same higher moral level (negotiations and compromise are better than war), or until the coming of the Kingdom of God in its fullness.