BBC's James Coomarasamy in Ukraine and Crimea and Romeo Dallaire on witnessing Rwanda Genocide

Twenty years ago today in Rwanda, began the worst genocide of the 20th century’s second half. Today, we'll breakdown how the genocide happened and the intentional decisions of the U.N. and Western powers not to stop it. We’ll revisit a talk from 10 years ago with former Canadian General Romeo Dallaire. He was head of the U.N. peacekeeping team in Rwanda during the 1994 genocide and he’s author of the book Shake Hands with the Devil: the Failure of Humanity in Rwanda.

Pro-Russian demonstrators have taken over government buildings in Donetsk in eastern Ukraine. They say they want to hold a referendum and vote on whether to become a part of Russia. We’ll discuss eastern Ukraine with the BBC’s James Coomarasamy. He’s just back from the region.

PHOTO: Two wailing and distraught Rwandan women are carried away to receive help during a public ceremony to mark the 20th anniversary of the 100-day genocide Rwandan genocide, at Amahoro stadium in Kigali, Rwanda Monday, April 7, 2014. (AP Photo/Ben Curtis)

On April 7, 1795, France adopted the metric system. As late as 1920, only about 25 percent of the world’s population was using it. But today, it has become the accepted system of measurement just about everywhere—except the United States. Historian John Schmidt tells us the story.