Actually GDI is a conglomeration of wealthy nations that withdrew their identity to create a global one world power in response to the ecological disaster of Tiberium.
An extra-terrestrial toxic crystal that has turned the Earth's ecology into an uninhabitable wasteland.
They are corrupt and ignorant of the science behind tiberium and the alien artifact known as the Tasitus which contains vital information of the purpose of the crystal.
GDI, is the global government of Earth. It was founded in accordance with the United Nations Global Defense Act , on the date of October 12, 1995, as a formalized military branch of the United Nations and evolved into a supra-national state in its own right. GDI's initial goal was to preserve world order by combating global terrorism, epitomized by its nemesis the Brotherhood of Nod, but eventually outgrew its original mandate to become a world government.
They did not become a world power until the events of the second tiberium war.