BERKELEY, Calif. — Growing up, Guneeta Singh Bhalla heard a terrifying story from her grandmother. In August 1947, as British India was being partitioned into independent India and Pakistan, her grandmother fled Lahore, in what was soon to become Pakistan, for Amritsar, in what was soon to become India. All around her was carnage. Clutching her three young children, she looked out the train window to see bodies strewed along the tracks. The memory haunted her until she died.

For years afterward, Ms. Bhalla regretted not recording her grandmother’s story, and it spurred her to begin recording other people’s memories of that time. The project, known as the 1947 Partition Archive, has grown far bigger, far quicker than she ever imagined. Since its inception here two years ago, its dozens of volunteers have video-recorded 647 oral histories from more than seven countries and stored them digitally. It describes itself as “a people’s history” of that wrenching time.

“It’s something that’s been brewing in my mind since high school,” recalled Ms. Bhalla, a research physicist who is now 34, about the same age as her grandmother in 1947. “As I was growing up, it was always in the back of my head, and bothersome, as family members were passing.”...