However by the time the 23rd century was reached, genetic engineering and cybernetics were in common use, and Earth's population had reached 23 billion. Consequently, a resource and overpopulation crisis was developing.
Earth's corporate factions who supported the capitalization of genetic engineering and cybernetics were opposed by those who saw this as a degeneration of the human race. These groups included humanist factions as well as religious conservatives who resorted to terrorism in these turbulent times. The conflict was resolved by the creation of the United Powers League, which generally supported the humanist philosophy and controlled all nations except for a few volatile Latin American states. The UPL banned many religions and made English the world-wide language.
The UPL proceeded to arrest and kill many people who opposed its "divinity of mankind" philosophy (which included "purity" from cybernetics, mutations, and so forth). It was during this time that Doran Routhe set up the colonization of the Koprulu Sector. Contact between the colonists and Earth was seemingly lost, and the Koprulu Sector Terrans could not have found their way back to Earth.
With the discovery of the Protoss and Zerg, the United Powers League reformed to become the United Earth Directorate and launched an invasion of the Koprulu Sector, ostensibly in an effort to protect itself from the distant aliens. The invasion was repelled by a tenuous alliance of the Sector's powers.
For more information see Earth on the parent site