The medium itself makes it difficult for Youtube series to be good history. It mostly caters to casual viewers who want to be entertained as well as taught, and to be successful you typically have to present simplified stories in short-ish videos with attention to animation/humour and little room for detail or nuance. I wouldn't recommend turning to Youtube to learn about history. Most of the big channels are of very doubtful (or at best uneven) quality, and this applies especially to the most popular ones. Their creators have proven to be good at creating a successful Youtube channel. That says pretty much nothing about the reliability of their content.

With that in mind, the best Youtube channels will be those that pay academic experts to help them with their work. Kurzgesagt is very conscientious about this, and these days actually provides links to the "footnotes" of their videos, which are all vetted by expert consultants; unfortunately they rarely touch on historical topics. TED-Ed also does good work collaborating with professional scholars, resulting in excellent videos like those on Roman social life with Ray Laurence of the University of Kent. But these are big channels with a lot of money behind them, and no specific focus on history.

So where do we turn? It's hard for any single person to vouch for an entire channel, and even the best channels will have episodes that make experts' blood boil. But I know that The Great War occasionally invites outside experts to write their scripts for them, resulting in high-quality content like the video on the Arditi. Also, Invicta is very good about getting historians to proofread/consult on their scripts, and is willing to take criticism on board, as I can attest from my work on their episodes on Sparta and on maps in ancient warfare. (Fellow mod /u/cleopatra_philopater was the consultant on their Ptolemaic Egypt episode.) It would be great if other people could add channels that are known to rely on independent experts rather than on their own quick reading, and see if we can get a bit of coverage for the vast swathes of history you're interested in!

The Crash Course European History series is written by Bonnie Smith, who is a well-respected historian of Europe. The medium means it is brief (by definition a “Crash Course”), but the content is well-vetted. The content aligns to the AP European History course description so really doesn’t start until 1400ish, though. I’m the education consultant on this series and also have a MA in History. I’ve been impressed with how seriously they want to get it right