North Korea shelled South Korea's Yeonpyeong island Tuesday, killing two South Korean marines and injuring more than a dozen people. South Korea returned fire. Both sides claimed that the other fired first. While the South has engaged in past attacks – notably in November 2009, when it fired on a North Korean patrol boat, and in June 1999, when it sunk a North Korean vessel – history shows that Pyongyang is often the instigator. A 2007 report from the US Congressional Research Service documents dozens of provocations, ranging from low-level naval warfare to assassinations of South Korean cabinet officers. Here are seven examples of the North's military provocations over the past decade.