Both North and South Korea are technically at war, after a ceasefire halted the Korean War more than 50 years ago. Tensions reached a new high when the North torpedoed a South Korean warship in 2010, killing 46 sailors. The South blamed Pyongyang, but the North denied responsibility. Later that year, the North bombarded a South Korean island, the first attack against civilians since the Korean War. This does not win friends with South Korea’s big ally, the US.

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A South Korea Marine's K-9 self-propelled gun tank moves during an exercise to mark the first anniversary of North Korea’s artillery attack on Yeonpyeong Island, at Baengnyeong Island, South Korea, Nov. 23. Both Koreas are still at war, though a ceasefire has been in effect for more than 50 years.