How do we reconcile the wholesale slaughter of nations by Israel with the sword against the words of Christ?

“… for all they that take the sword shall perish with the sword.” (Matthew 26:52)

Not only men and women but children also:

“And we took all his cities at that time, and utterly destroyed the men, and the women, and the little ones, of every city, we left none to remain.” (Deuteronomy 2:34)

Were the Israelites truly in tune with the character of God? If not, then why does it appear that God Himself commanded such violent acts?