In summer blockbusters and other entertainment, the United States Armed Forces are almost always portrayed through the lens of their most elite units, such as the Navy SEALS or the Army Rangers. But while the special forces are heroes in their own right, they’re not the most irreplaceable piece on the board. That designation falls to the humble National Guard, the real backbone of America’s military. I’ve served in the Marine Corps, the U.S. Army, and the Idaho National Guard. In my deployments to Afghanistan, I found the Guard to be the best trained of them all. Numbering nearly 350,000 men...