From the Overview: "On January 19, 2021, the Trump Administration designated the Yemeni group 'Ansar Allah' (Arabic for 'the Partisans of God'), commonly referred to as the Houthis, as a Foreign Terrorist Organization (FTO) and a Specially Designated Global Terrorist (SDGT). In notifying Congress, (per 8 U.S.C. §1189), then Secretary of State Michael Pompeo identified that the Houthis were closely linked to Iran and that the designations were intended to hold the Houthis accountable for terrorist acts. The designations reportedly had been under consideration for months, though aid organizations repeatedly cautioned that designations would exacerbate what the United Nations presently considers the world's worst humanitarian crisis."
CRS Insight, IN11585
Congressional Research Service: https://crsreports.congress.gov/