Answer: South Korea and the United States
Notes: South Korea and the United States launched their largest-ever joint aerial drill exercise "Vigilant Ace-2017" on December 4 and will run till Dec 8, 2017. Around 12,000 US service members, including from the Marines and Navy, are joining South Korean troops. The joint exercise is designed to enhance readiness and operational capability and to ensure peace and security on the Korean peninsula, the US military had said before the drills began. The exercise comes after a week after North Korea said it had tested its most advanced missile as part of a weapons programme that has raised global tensions.
