It was Solomon who built up a professional army, for through taxation and trading he was able to accumulate sufficient wealth to pay for it (1 Kings 10:25-27). In times of national emergency the regular army was supplemented by conscripts. Recruiting officers went through the tribes on such occasions and were still in use at a much later date (2 Kings 25:18; 2 Chronicles 11:1).
Solomon also built up the fortified cities to protect the major highways into and through his kingdom and provided chariot units to defend the cities (2 Chronicles 1:14). Several rules for conscription were set out in Deuteronomy 20:5-9. People who had built a house but had not yet undertaken the religious ceremony of dedication; people who had not yet had the first crop from a newly planted vineyard; people who were betrothed but were not yet married; and people who had lost their enthusiasm for war (the elderly?) were exempted. This was not simply human treatment, but followed a religious conviction at the time which held that all undertakings had to be completed.
As the wealth of the kingdom declined after Solomon, it became increasingly difficult to put a professional army into the field. Towards the end of the monarchy and during the times of the Maccabees, the Jewish army reverted to a militia, and in New Testament times there was no army at all. The Jews were successful in the hill where surprise tactics and hand-to-hand fighting were in order, but they were much weaker on the plains where their enemies could muster chariot units. The God of Israel was therefore (incorrectly) reckoned to be a God of the hills rather than a God of the plains (1 Kings 20:23).