For me, it is obviously the United Kingdom of Great Britain and Northern Ireland. The impact they had on the world can't even be said. They even managed to replace the Latin which had replaced the Greek which had replaced the Phoenician which had replaced the Egyptian which... was probably the first language in the world... They also had a lot of play writers and oh boy.
Second is the Kingdom of Macedon, managing to make the Greek language the most spoken in the whole word for quite some time. They were spoken all the way from Central Asia to Southern Spain.
Third is the Roman Empire. I don't even need to say anything. The Roman Empire might as well be the most famous empire to have ever existed. It would've been in the 1st spot of my list but, because of their culture was stolen/inspired by the Greeks, I'm putting them in 3rd place.