They conquered Greece, because at the time Macedonia was ruled by Alexander the Great (and before him his father) who became a major figure in history as he has conquered vast areas from Greece to modern day parts of middle East and even Asia.
Because Alexander had a strong military background and was able to conquer Greece (which was only the start) with relative ease, he further expanded his empire during his lifetime. He did all of this at a relatively young age because he died at the age of around 35 or so.