So I had this History lesson and it kinda motivated me to write this entry.
Elijah wants to make new weaponry. So, he discovered the secret of Helios One power plant to use his own needs. However, even if he got out of the Brotherhood of Steel, he still belived in his plans. So, using more advanced technology can shape to a brighter future - the plan is to get the lost technology and use it to make new weapons. The technology is almost useless to the wastelanders, like the power armor - they can't use it unless they are a part of the Enclave/Brotherhood of Steel (as they teach how to use it). As the people founded the colony of the USA (and had to kill the native people using guns (there were about few hundred men who took several thousand people from the tribes, like the Aztecs)), the Brotherhood can defeat anyone who stands in their path, eventually protecting the lands from any attacker (as seen in Fallout Tactics).