Under what circumstance can the National Guard be activated?

The correct answer is that the National Guard can be activated when necessary. This option captures the broad scope of situations that might require the deployment of the National Guard, which can include emergency situations such as natural disasters, civil unrest, or other crises that require additional support.

While the National Guard can indeed be activated during wartime or at the request of state governors or the federal government, it is important to note that the phrase "when necessary" encompasses a wider range of scenarios. This flexibility is crucial because the National Guard is often called upon for various domestic missions, not just in times of war or at the request of higher authorities. The idea is that the activation is contingent upon the needs of the community or the state, making it a response-driven activation.

In contrast, the options that imply specific conditions like "during war" or "in peacetime" do not capture the full extent of circumstances under which the National Guard can operate. The option about activation "upon request" is also too narrow since it overlooks situations where activation may be mandated by pressing needs rather than a formal request process.