The only good "history" channel left is the Military channel.
The only reason for that is because the History Channel used to practically just show WW2 and occasionally WW1 programmes and it had the nickname of the 'Riddler/national socialist Channel'.
They got lots of complaints because anyone interested in non-WorldWar documentaries had very few places to see those, and History didn't show them as much.
So, they created Military History and stuck all the war programmes on there, which they have thousands of. Then they were left with The History Channel.
And it turns out that it is much cheaper to make 'reality documentaries' than History ones, and they also get more views. They're cheap and make lots of money.
And its so good that its copied by other channels too. Dave, a UKTV channel which used to just show BBC repeats now makes its own 'reality documentaries'.
My favourite documentary channel which is entirely untouched from 'reality documentaries' is Eden, which is a channel run by UKTV and shows nature documentaries. But UKTV doesn't make loads if money, so it just buys and shows old documentaries from other bigger channels, like BBC, ITV or Channel 4. So unfortunately, the only good places here to watch proper documentaries doesn't make its own. And its poor enough that it resorts to switching to Teleshopping at night, so you can't find a nice documentary to watch in bed.