Why can the National Guard be called up for duty without a declaration of war?

The National Guard can be called up for duty without a declaration of war due to its dual state-federal status. Under Title 10 of the U.S. Code, the federal government can activate the National Guard for various emergencies, including natural disasters, civil unrest, or national security threats. This allows for a rapid response to situations that require immediate military assistance without needing formal war declarations. Additionally, governors can mobilize the National Guard for state-specific emergencies, further enhancing its flexibility and availability.