The Supreme Headquarters International Law Enforcement Division was created as a global peacekeeping force, although their primary funding comes from the United States. While SHIELD was the brainchild of Nick Fury in its early stages, the government took the idea and originally created the organization without him, casting Rick Stoner as the first director of SHIELD, until his assassination led to Fury getting the job he was always meant for.
After the Deltoid Crisis, when the majority of SHIELD agents were secretly replaced by advanced LMDs, the organization disbanded. Nick Fury recreated SHIELD as a five man team of his closest allies, before slowly rebuilding the group back to its former numbers, now known as the Strategic Hazard Intervention Espionage Logistics Directorate.
Several temporary directors of SHIELD have replaced Fury in the past, when he was believed dead or after his fall from grace, including Dum Dum Dugan, Sharon Carter, G.W. Bridge, Maria Hill, and Tony Stark. Norman Osborn deconstructed SHIELD again when he created HAMMER for the Thunderbolts Initiative, but Steve Rogers recommissioned the old agency in the aftermath of Osborn's Dark Reign, now known as the Strategic Homeland Intervention, Enforcement and Logistics Division.
Most recently, SHIELD was corrupted from within by the Hydra Supreme version of Steve Rogers. The SHIELD Act allowed the U.S. government to turn full authority of the state over to the director of SHIELD in times of extreme crisis. Evil Steve Rogers manipulated himself into that position and manufactured such an emergency situation, tricking America into ceding control of its own government to him and Hydra. Although the Hydra Supreme was eventually overthrown and defeated, SHIELD's reputation was too tarnished by these events to continue, and the organization was dismantled.