SHIELD
SHIELD (an acronym for Strategic Homeland Intervention, Enforcement, and Logistics Division) is an international defense organization with both covert and military branches. It specializes in defending Earth against abnormal threats, such as alien invasions.
Organization
SHIELD has a heirarchical command structure. The highest-ranking member of the organization is the Director, currently Nick Fury. Above the director is an international oversight council with representatives from the United States, United Kingdom, Russia, and China.
Resources
The sources of SHIELD's funding aren't clear, but the organization has a prodigious budget capable of building multiple helicarriers with full airwings in addition to fielding numerous intelligence agents, operating a substantial military force, and funding major electronic surveillance operations.
Threat Assessment
SHIELD is a credible threat to virtually any nation on Earth. It is the primary defense against threats from other worlds, but even with its cutting-edge technology and resources, it does not appear to be a match for a major interplanetary invader.