Judges 3:2

only that the generations of the children of Israel might know, to teach them war, at the least such as beforetime knew nothing thereof:

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

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.

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

only in order that the generations of the sons of Israel might be taught war, those who had not experienced it previously).

( this was only so that the generations of the children of Israel might be taught to know war, at least those who had not formerly known it),

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

only that the generations of the children of Israel might know, to teach them war, at least those who knew nothing of it before: