When warfare took place it was normally at a time when food was available to live off the land and when weather conditions made war feasible (2 Samuel 11:1). So far as the Jewish army was concerned, the central “administration” unit (Numbers 2:17) was surrounded by four divisions (Numbers 2) and was preceded by an advance guard.
There was no “declaration of war.” War started as soon as one army entered another’s territory. Then there was a parley. The invader offered the defenders their lives in return for their service, and sometimes there were other conditions as well. If the defenders gave in they were either enslaved or forced to pay protection money. If the defending army refused their opponent’s terms, the attack on the city would begin. The city’s water supplies were cut off if this was possible, and its food supplies were blocked off by completely surrounding the city, sometimes with siege walls. The surrounding army might have to withdraw if sallies from the city were successful (Judges 20:31-31), because of illness and death (caused by God) in the camp (2 Kings 19:35-36), or because there was relief on its way from another quarter (2 Kings 24:7). The weather might also become so bad that the attacking army be forced to retire until later date.
If the siege war was successful, the women and children were enslaved, all the men were killed, booty was taken to give the soldiers their pay, and the city was then burned to the ground.
The Assyrians were particularly cruel in this respect. The chief men of the defeated city were brought to the gates to be tortured, blinded, and burned alive. Scribes counted the number of dead from the severed heads brought to them as tallies.