Census, soldiers and war

Take ye the sum of all the congregation of the children of Israel, after their families, by the house of their fathers, with the number of their names, every male by their polls;  From twenty years old and upward, all that are able to go forth to war in Israel: thou and Aaron shall number them by their armies.  And with you there shall be a man of every tribe; every one head of the house of his fathers.
Numbers 1:2-4

God commanded Moses to conduct a census the year year after they left Egypt. God wanted the Israelites to carry out the census by families and to to enlist sons who were 20 years old and above and who were able to go to war.

The Israelites were always at war with their neighbours till this day and their military strength is well known.