US and the UK are assisting in the blockade of Yemen. The US, UK, Germany, France, China, Canada, and Al Quaeda are also providing arms sales and/or logistical support to the Saudi Arabia led coalition. Wikipedia source, but I'll gladly edit if you can disprove any of their sources.
This crisis is entirely man-made. Saudis are crushing the Houthi rebels, indifferent to civlian starvation and disease.