The problem that occurs is when one of the planet's citizens decides that despite all they have seen in the universe, their planet should develop weapons for defense against the potential unknowns. This proposal is met with staunch opposition, as it's believed that any space travelers that can approach from beyond what they've explored should have similar advances brought about by similar peace. The unlikelihood of a battle negates the need for weapons, something never necessary in this world. With a small contingent of like-minded developers who hear his idea and concur, the weapons are built, regardless of its unpopularity, on another planet in their solar system. His intuition is correct, as their world is approached by a hostile invading force. A war ensues, and the entire planet unifies in support of the defense efforts, the first battle of any kind this world will ever know.
After a lopsided victory via superior technology, the world celebrates a new hero, but the battle changes his outlook on the entirety of the universe. He now knows there are multitudes of peaceful worlds that may face hostile invasion from the unknown depths of space. With global support, he embarks upon a mission to travel throughout the universe in search of hostile worlds that exhibit the potential to leave their atmosphere, accompanied by their savagery. His mission spreads carnage upon those planets he deems hostile, to prevent the potential attacks against peaceful worlds that are found and preserved. He comes in conflict with his daughter, who is born and raised during his travels, and later his son, born after his daughter's defiance, after they are exposed to and horrified by their father's mission to ensure peace in the universe.