When mankind first reached for the stars, it was built upon the foundation that we had built on the backs of conflict throughout the ages. Rocketry, the crudest form of space travel was originally developed for warfare. Times of great technological advancement have always been proceeded by times of internecine conflict. Medical advancements and marvels both technical and architectural show in their core design mankind's flawed tendency of the application of military force.
When first we reached the stars and discovered them to be empty save for ourselves, those who had once dreamt of claiming the stars by fire and sword were left without an external foe to turn their tools of war towards. Those who had spent their lives dreaming of carving their names in the annals of history and anointing their immortality in the blood of their enemies turned once more to that most ancient of foes, themselves.
True immortality, the ability to live forever unchanging in a constantly changing universe is theoretically possible according to most scientists. While any technology that would allow such to occur is still far off in the distant future, there is still the age old immortality of the past. Names stand in our collective conscious of those ancient warriors who etched their memory into our past. Men both great and terrible are in fact still remembered to this day. Names such as Genghis Khan, Erwin Rommel, and Alexander the Great are still remembered even though their deeds and lives are now in some cases more than a thousand years old.
Humanity as a collective whole does not remember the brilliant minds who developed the first working computer, but it does remember those who built the first atomic weapon. That desire for immortality is in part, what has driven the Alliance and Coalition to the very precipice of that most terrible human endeavor once again.
*Excerpt from Visiting Humanity in the Stars, Brinkley Publishing, Heinlein, 2620 edition.