Until the recent incident involving a defecting soldier, tensions between the United States and North Korea had cool slightly, largely because the communist regime hasn't committed any so-called "provocations" — ballistic missile and nuclear tests — in more than two months.

Under the North's young leader, Kim Jong Un, such incidents have increased significantly as his nation seeks to improve its ability to strike targets with nuclear weapons. That effort has included dozens of ballistic missile tests and four underground nuclear detonations during his tenure, which began in late 2011 after the death of his father, Kim Jong Il.

This timeline, inspired by a graphic made by the NPR Visuals team, shows these provocations since 2006, when the regime tested its first nuclear weapon: