On February 21, 1955, Sadako Sasaki, a 12-year old girl from Hiroshima, Japan, was hospitalized with leukemia, brought on by the atom bomb dropped on that city in 1945, when she was 2. She was about one mile away from Ground Zero at the time. The bomb had taken a decade to do its damage to Sadako, but the damage was done. Doctors gave her a year to live, if that.
Sadako had other ideas. An old Japanese belief holds that a person can be granted a wish by making 1,000 origami cranes. (A group of 1,000, held together with string, is called a senbatsuru. Thus the post title.) Sadako had a wish. She wished to get better. On August 3, she was given a crane by her friend, Chizuko Hamamoto. At that, she resolved to fold the necessary cranes, and spent hours every day working towards the 1,000-crane mark. There was a lack of the amount of paper she would need at the hospital, but Sadako made do however she could, with whatever kind of paper was available. Medicine wrappings, the wrapping paper from other patients' get-well presents, Chizuko would bring paper from school, whatever worked.
Unfortunately, after 644 cranes, Sadako ran out of time. She died on October 25. Her classmates folded the other 356, and laid them as well as her own to rest along with her. (Although the Hiroshima Peace Memorial Museum maintains that she made it to 1,000.) A statue of her stands at the Hiroshima Peace Memorial, where cranes continue to be placed to this day. There's a good chance that, if you think back, you'll recall reading the story in school once.
Given that Japan is, once again, dealing with nuclear radiation, it feels appropriate to bring up the story. While far and away the best thing you can do to help from home is always going to be to send money (hint hint), here's an instructional video on how to make an origami crane.
You know. Just in case.