I myself judge individuals on an individual basis. I have my own feelings concerning whether nations or societies are good or evil. But my feelings are formed by my experiences with individuals and my understanding of history.
Just like our father Abraham begged Hashem to not destroy Sdom and Amora because there may be 50 righteous men in Sdom, we should pray that Hashem would not destroy whole nations, the righteous along with the wicked. This is my understanding of how we should view these kinds of events.
Each individual is capable of doing repentence and being judged favorably in the eyes of Hashem. But, as Chaim and others will point out, there is a calculation which Hashem makes when he will issue a decree against an entire people, nation, and country. I am not capable of explaining this calculation because I believe it is beyond human understanding.
When we witness divine retribution we are supposed to learn something and take the lesson to heart. In the Torah portions which we have been reading the last couple of weeks we learn about the 'plague' of Tzaarath. In some respect Tzaarath are very bad, it is a physical/spiritual affliction sent by Hashem against a Jew who has spoken Lashon Hara or committed similar aveirahs. Tzaarath can also afflict a house... But even though it is an affliction it is sent in order to bring about teshuva in the afflicted individual.
When Tzaarath afflict a house it is for two reasons. One reason is that the house is consumed by impurity {Tuumah}... Another reason is that the house contains valuables hidden in the walls. A house with Tzaarath is torn down according to the laws of Tzaarath... Once torn down the treasures in the home are available. So there are two reasons, the impurity is so bad that the only solution is to destroy the home.... But there is also the good aspect that the home is destroyed and thus exposes the reward...
I hope to post soon in the Torah section some of the lessons I have recently learned from the laws of Tzaarath...
http://www.torah.org/learning/mlife/chapter6-7a.html
Leviticus 14 discusses the plague of leprosy ("tsara'as") as it pertains to houses. If a person finds certain colored spots on the stones of his house, he must notify a priest who then comes to the house to determine if the spots are leprous. During the course of examination and purification, the afflicted walls of the house are generally broken down and the leprous stones removed and replaced.
Now the Sages tell us that leprosy is visited upon individuals as punishment for certain sins, one of the primary ones being gossip (Talmud Erchin 16a). Yet here, note the Sages, there was a silver lining to the affliction. During the forty years Israel dwelled in the wilderness, the inhabitants of the Land of Canaan, anticipating Israel's eventual invasion, stashed away most of their treasures. Much of it was stored behind false walls in their homes. Thus, when the priest would destroy the leprous wall, a treasure would be discovered within (Vayikra Rabbah 17:6, brought in Rashi to v. 34).
http://www.torah.org/learning/ravfrand/5758/tazria.html