In a bold speech on Thursday, NATO Secretary-General Mark Rutte revealed a plan that could shake up the priorities of European governments. Speaking at a meeting in Brussels, Rutte argued that European countries need to stop focusing so much on social welfare and instead pour more money into their military. His message? To stay safe, Europe must increase military spending—no matter the cost.

Rutte, addressing an event organized by the Carnegie Endowment for International Peace, said that...