The Global Defense Initiave began as a secret alliance of first world countries under the UN umbrella. GDI's mission: To contain Tiberium, reverse its spread and fight the sinister Brotherhood of Nod.
Over time, power and sovergienity have been gradually seceded to GDI and the identities of the member nations have faded. In 2046 process has reached its final stages: while their are still technically individual member nations, the reality is that GDI has become a unified political and military super state.
— Command & Conquer: Tiberium Wars