The State Department has designated a group known as Ansarallah, also called Ansar Allah or Partisans of God, as a Specially Designated Global Terrorist. This decision is based on their involvement or risk of involvement in terrorist activities that threaten U.S. national security and foreign policy. The order prevents any advance notice to the individuals affected, as this could undermine the government's ability to effectively block their assets. Michael R. Pompeo, who was the Secretary of State at the time, signed the order on January 12, 2021.
Simple Explanation
The State Department decided that a group called Ansarallah is very dangerous and might do bad things that could hurt people or the U.S. They did this to help keep people safe, and now some rules will stop them from using their money for bad things.