Forerunner territory

"Some of the ideals are factually true. The Forerunners were sophisticated above all other empires and powerful almost beyond measure. Our ecumene spanned three million fertile worlds. We had achieved the greatest heights of technology and physical knowledge, at least since the time of the Precursors, who, some say, shaped us in their image, and rewarded that image with their breath." (Halo Cryptum; Ch.1)

“It was one cause of our war,” the Didact said. “Not the primary cause, however. Humans resented Forerunner expansion outward. For fifty years, scattered through the galactic arm, humans probed our settlements and positions. Then they allied with the San’Shyuum, combined their knowledge, and created weapons against which my warriors had little defense.”
“Settlements? I thought Forerunners didn’t need new planets—that we’d achieved maximum growth.”
The Didact sighed. “There are many things Builders do not teach to their young,” he said. “Earlier displacements around Orion and in toward galactic center forced us to move native populations from their home regions to new, outer systems. The Librarian and her staff cataloged and searched for the most appropriate matches, those stars most like native suns…..”
“You shuffled planets?”
“Yes,” the Didact said. “Humans are naturally purists. They resent having to live with other species. In fact, they’re among the most contentious, bigoted, self-centered…..” He looked back at Riser and Chakas. “I never understood how my wife tolerated them.” (Halo Cryptum; Ch.11)