China's missile force has Guam in its sights. The US military just took a big, first-of-its-kind step toward strengthening its defenses.

Screengrab via Missile Defense Agency

• The US shot down a ballistic missile for the first time from Guam in a major test this week.
• The event comes as the Pentagon increasingly looks to protect key military infrastructure on Guam.
• Guam would almost certainly be a target in a war with China, which has missiles that can reach the island.