Judges 3:2

It was only in order that the generations of the people of Israel might know war, to teach war to those who had not known it before.

(he did this only to teach warfare to the descendants of the Israelites who had not had previous battle experience):

This was to teach the future generations of the Israelites how to fight in battle, especially those who had not fought before.

He did this to teach warfare to generations of Israelites who had no experience in battle.

in order that the generations of Israel would know war, to teach those who had not experienced it before):

Only that the generations of the children of Israel might know, to teach them war, at the least such as before knew nothing thereof;