Technological achievement
Early faster-than-light drives are made in the Ligera Band after hyperparticle flows are discovered. These utilize devices to catch the particles like sails.
The faster-than-light technology of the time was extremely slow and primitive for modern standards. It could take a week to travel from Harmonia to Burrwos with these devices. Although they were slow, inefficient, and primitive, these inventions were absolutely game changing as they allowed the civilizations in the Ligera Band to contact each other for the first time. These civilizations started trading (and fighting) with each other soon after and created the first interstellar communities. Other planets also adopted interstellar technologies and expanded further.