As time has gone on, Mr Annan’s peace plan has continually been ignored by both sides in the conflict, as Assad’s government continue to bombard the opposition with shelling in key cities, while reports have been coming through of rebels executing their prisoners.
In a news conference, he also accused the international community of "finger-pointing and name-calling".
He said, "It is impossible for me or anyone to compel the Syrian government, and also the opposition, to take the steps to bring about the political process.
"Syria can still be saved from the worst calamity - if the international community can show the courage and leadership necessary to compromise on their partial interests for the sake of the Syrian people - for the men, women and children who have already suffered far too much."
The Syrian foreign ministry expressed “deep regret” at Annan’s departure, a sentiment echoed by present UN Secretary General Ban Ki-moon.
But Mr Annan saved a big portion of the blame for the United Nations, who remain deeply divided over what to do with Syria. The UK and USA have been fighting for tougher sanctions on President Assad, but they have been continuously blocked by Syria’s allies Russia and China.
UK Foreign Minister William Hague has announed that international efforts in Syria will continue, despite Mr Annan’s departure.