There are some great channels on Youtube. If you want to watch old documentaries, new ones like the DW channel from Germany, history channels which actually cover all sorts of history. Social, economic, political, military from every period of the recorded record. Science channels, nature documentaries, cosmology etc,etc.
Seeing as television in the US and UK has been dumbed down so much it's a welcome relief. The BBC for instance scrapped QED and turned a flagship science programme Horizon into a shadow of itself. While current affairs programming has also been reduced, and programmes on the high arts also slashed in favour of reality TV garbage, sewing and baking contests.
The BBC produced such immense series as Civilization, Life on Earth, The Shock of the New and great drama series like I, Claudius and even it's commercial competitors like ITV produced The World at War. Not anymore aside from the BBC Natural World unit.
In the USA PBS is the last bastion of any decent programming. I'm sure you've heard of Ken Burns. His works are masterpieces of education all presented with a light informative touch and often reveal the lives of those who lived through historical events.
His last series The Great American Buffalo was wonderful. Intertwining the near extinction with the way the native tribes were treated, the advent of the railways, the role of politicians both good and bad, the changing attitudes of former hunters and the way the US has transformed as a result. And the revival however small of the species.