The Antwerp Conference Bombing
If you've seen the 2-part episode "Homefront and "Paradise Lost", you might know what I'm talking about.
In "Homefront", the Antwerp Conference is bombed. It's blamed on the changelings. Sisko and Odo go to Earth to investigate and help Admiral Leyton implement new security measures to protect them from the changelings. Then at the end, the power grid goes out all over Earth and martial law is declared. Now Starfleet has armed security officers all over Earth blood testing citizens at random.
In "Paradise Lost", Sisko and Odo learn it's all part of a coup Leyton is plotting to seize control of Earth. And Sisko demands Leyton's resignation.
I can't help but wonder something. It's about the Antwerp Conference bombing; Was it staged by Leyton? It wouldn't surprise me if it was.