When dealing with a civilized nation, we expect that such a nation will recognize the value of just and equitable dealings.
people? Destined for Gehenna
When we see a primitive people who rob and plunder, we attribute their actions to their savage and uncultured nature. But when dealing with a civilized nation, we expect that such a nation will recognize the value of just and equitable dealings.
When a highly developed society is gripped by a belligerent spirit of conquest and oppression, like the Persians who subjugated the Jewish communities under their control, then they are destined to be judged harshly by the Eternal Judge.
The expression "consecrated and destined for Gehenna indicates that this judgment is not due to a primitive nature, but rather the result of a willful choice. The cultured Persians should have chosen the path of goodness, but instead chose the path of violence and persecution.
Forgetting G-d
This idea may also be heard in King David's call for Divine justice against evil nations:
"The Eternal has made Himself known, executing judgment... The wicked will return to the grave - all nations who forget God." (Ps. 9:17-18)
This portrayal of "nations who forget G-d" indicates that in fact these nations ought to remember G-d. They have the potential and sophistication to know G-d and emulate His ways of kindness and justice. But instead they chose to pursue a path of moral treachery, so they are called "nations who forget G-d."
(Adapted from Rabbi Avraham Y. HaKohen Kook zt"l ,Ein Eyah vol. I on Berachot 8b (1:111))