Who were the 600,000 men of war in Israel?
The 600,000 men of war were Israel's counted fighting men, described as young and unmarried, numbered from twenty years old and upward. Because they murmured against God, that generation was excluded from the Promised Land, except Caleb and Joshua. They were the ones whose carcasses fell in the wilderness.
Les explains that all Israel was counted, and from those numbers he estimates there were anywhere from three to seven million people. Altogether there were over 600,000 men of war—young men, unmarried. Once you compute all their relatives and families, you can easily get five million people. He compares this to the Dallas–Fort Worth metroplex, which had only a little over three million, and asks us to imagine that multitude in the wilderness of Sinai. He notes that the verse specifies the whole number from twenty years old and upward who murmured against God, and that they would not enter the land except Caleb and Joshua.