Tensions between South Korea and North Korea reached their highest point since the Korean War after two attacks against South Korea, threatening to spiral into a larger conflict at year’s end.

The first attack came March 26, when a South Korean warship sank after being hit by what military officials claim was a North Korean torpedo.

A South Korean-led international investigation, which included analysts from the U.S., Australia, the United Kingdom and Sweden, found that a North Korean submarine came into South Korean waters and fired the torpedo, splitting the warship in half and killing 46 sailors. North Korea repeatedly denied any involvement in the attack. Speculation was rampant, with many South Koreans blaming the incident on structural failures in the ship, a collision with a reef, and a plot by South Korean politicians to garner support during upcoming elections.

South Korea and the U.S. responded to the incident by holding exercises meant to show unity and military strength.

On Nov. 23, North Korea bombarded a populated island near the maritime border between the two countries, its first attack on South Korean civilians since the end of the Korean War. Four people died in the shelling, which North Korea claimed was a response to a South Korean military exercise. The South’s lackluster military response — 80 shells fired in response to 170 fired by the North — led to the sacking of the minister of defense and a promise by his replacement to respond to future provocations with airstrikes.