Cuba (along with Syria, Sudan, and Iran) compromise the State Department's list of State Sponsors of Terrorism - which I would assume is the origin of their being on that list.
America has been living under the shadow of imminent Cuban aggression for 50years. There have been Cuban attempts to invade America and numerous assassination attempts on the US president by Cuban agents.
And their chemical weapons kill 1000s of Americans after being secretly delivered from Canada.
Cuba, Iran, North Korea, Libya, Syria, Sudan, Afghanistan, Lebanon, Somalia, Iraq, Yemen, or Algeria