I think that would be Iran. We completely defeated MeK terrorist group inside Iran (Islamist-Marxist Iranian terrorist group, I know, that's a weird combination) who killed more than 10,000 Iranians (including senior officials, president, head of parliament) in 80s. We kicked them out of Iran, they went to Iraq and sided with Saddam Hussein against Iran, and launched their last major offensive from Iraqi border in 1988 to capture Tehran, fell in a huge ambush, lost 4500 in just 2 days (
Operation Mersad), and Iran was cleansed from their presence forever.
They did terror attacks in Iran that TTP could only dream of, in first years of revolution and war when country was still in chaos.
Now their remnants are living in misery in west and in a camp in Iraq.
As you'd expect, U.S and Europe de-listed them from their terror group list, because obviously, terrorist attacks are fine as long as they target west's enemies.