People from Nuba Mountains tribes perform dancing to mark the International Day of Peace in Khartoum, Sudan, Sept. 21, 2019. The International Day of Peace is observed around the world on Sept. 21 each year. (Photo by Mohamed Khidir/Xinhua)

People from Nuba Mountains tribes perform dancing to mark the International Day of Peace in Khartoum, Sudan, Sept. 21, 2019. The International Day of Peace is observed around the world on Sept. 21 each year. (Photo by Mohamed Khidir/Xinhua)

People from Nuba Mountains tribes perform dancing to mark the International Day of Peace in Khartoum, Sudan, Sept. 21, 2019. The International Day of Peace is observed around the world on Sept. 21 each year. (Photo by Mohamed Khidir/Xinhua)