At a moment when the United States military is stretched thin by a grinding confrontation with Iran — one that has consumed a third of its cruise missile stockpile and drawn forces away from Europe and the Pacific — Defense Secretary Pete Hegseth has undertaken one of the most sweeping purges of senior military leadership in modern American history. The simultaneous pressure of external conflict and internal upheaval raises a question as old as statecraft itself: can an institution remake itself while it is already at war? The answer, history suggests, is rarely without cost.