What caused the South Sudan famine of 2017?

Sources:

Beaubien, Jason. "Why The Famine In South Sudan Keeps Getting Worse." NPR. NPR, 14 Mar. 2017. Web. 10 Apr. 2017. <http://www.npr.org/sections/goatsandsoda/2017/03/14/520033701/why-the-famine-in-south-sudan-keeps-getting-worse>.

"Civil War in South Sudan." Council on Foreign Relations. Council on Foreign Relations, 10 Apr. 2017. Web. 10 Apr. 2017. <http://www.cfr.org/global/global-conflict-tracker/p32137#!/conflict/civil-war-in-south-sudan>.

"Famine Declared in Part of South Sudan's Unity State." Al Jazeera. Al Jazeera, 21 Feb. 2017. Web. 10 Apr. 2017. <http://www.aljazeera.com/news/2017/02/famine-declared-part-south-sudan-unity-state-170220081516802.html>.

"South Sudan Famine: Eating Water Lilies to Survive." Al Jazeera. Al Jazeera, 28 Feb. 2017. Web. 10 Apr. 2017. <http://www.aljazeera.com/news/2017/02/south-sudan-famine-eating-water-lilies-survive-170228050621672.html>.

https://www.washingtonpost.com/world/africa/famine-declared-in-south-sudan-with-100000-people-facing-starvation/2017/02/20/f6eb9336-f778-11e6-aa1e-5f735ee31334_story.html?utm_term=.ee4a7f57e5f5

https://www.pri.org/stories/2017-02-20/south-sudan-declares-famine-aid-groups-lament-man-made-tragedy

http://www.bbc.co.uk/newsround/39107125