April 12, 2016 12:10 PM EDT

A new report by Amnesty International found that at least 1,634 people were put to death worldwide last year, a 50% increase from the year before.

The vast majority of the surge was driven by just three countries — Iran, Pakistan and Saudi Arabia. And the human rights group’s numbers don’t even include China, which is believed to execute thousands of citizens behind a veil of secrecy.

Figuring out why 2015 in particular saw so many people put to death isn’t easy. Watch the video above to find out more.


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