Final answer:
The first line of emergency response typically comes from local or tribal resources and local mutual aid agreements, such as EMS, fire departments, and police that are immediately available to respond.
Step-by-step explanation:
In most incidents, the source that provides the first line of emergency response and incident management resources is local or tribal resources and local mutual aid and assistance agreements. These local responders include emergency medical services, fire departments, and police departments funded by taxes, ready to react without additional charge. The local level is critical in managing immediate responses before higher levels of support are mobilized, such as state resources or federal government agencies.
In large-scale emergencies where the capacity of local responders might be exceeded, the next layers of support come from state and federal levels. For example, states can call upon the National Guard to assist during emergencies. As the scale of an emergency grows, if required, the involvement of federal agencies can be seen under acts such as the Robert T. Stafford Act, which enables federal assistance. However, this support is typically requested after local and state resources are deemed insufficient.