The Fta Tei is a race that was a collateral branch of one of the human race's multitude of descendant species. The Fta Tei, however, knew nothing about their origins on Earth.
When the Assiti used their mastery over spacetime to make "art" (which included causing the transportation of the West Virginian town of Grantville into 17th-century Europe), the Fta Tei repeatedly warned the Assiti about the consequences of their "artwork". Ultimately, the Fta Tei exterminated the Assiti race for endangering time and space.