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.