Third World War
Very little is known about this human conflict that eventually resulted in the complete destruction of the "post-modern" human society in the 21st century.
What is known however, is that human superpowers fought over natural resources such as oil in this war that later climaxed into a global nuclear fire. A human international organization known as the United Nations was also disbanded during the conflict since it failed to bring the fighting factions into the negotiation table to find a peaceful end to the crisis.
Historians studying this particular period in human history seem quite confident that the war started out exclusively between two large nation states over the control of natural resources. Theories have suggested however, that smaller nation states erupted into internal chaos and general upheaval shortly after stocks of the needed natural resources had completely ran out on a national level.
The resulting nuclear exchanges between the larger nation states devastatated many continents quite badly, although there were areas on Earth that were left almost completely untouched by the destruction. Such continents where a nuclear holocaust was diverted was Africa, Scandinavia and parts of Central Europe and the Pacific Ocean. According to the Gigerdian anthropologist Ewar Q. Devel, it is possible that the entire human society had been so dependant on natural resources that once resources started to run out, a total collapse of societies followed. Dr. Devel also speculates, that at the beginning of the war only the strongest nation states on earth controlled these natural resources and once the despair grew, they eventually engaged each other over the remaining material.
States that survived the nuclear exchanges were forced to new ways of acquiring power supplies, food, drinkable water, working infrastructure etc. in the post-apocalyptic world. The ensuing "period of survivalism" also continued the trend of primitive "kill or be killed" - tactics that were so typical of the human race during the earliest centuries of their existence.
Dr. Devel also wonders why evolution itself left such a species so bent on self-destruction and blatant exploitation of its natural habitat alive. It does seem clear, that despite these negative qualities in the collective psyché of the human race, it managed to somehow survive even after the war.
Of course everything changed for the best once the humans established contact with the Lihters. The Lihters showed the humans a new, peaceful way of interacting between each other and their planet - thus making them a truly commendable member of the intergalactic community.