US armed forces; US military
Refers to the United States military as a whole, including all branches. Commonly used in news and formal contexts.
There is a US military base in Okinawa.
The US armed forces have introduced the latest equipment.
Many US forces are still stationed in Okinawa today.
The US military withdrew from that region.
米軍 refers to the US military as a whole, whereas 在日米軍 specifically means the US forces stationed in Japan.
米軍 is the United States military, while 自衛隊 is Japan's own Self-Defense Forces, a completely different country's armed forces.
US military base
Compound of 米 (べい, 'America') and 軍 (ぐん, 'military').