Like many individuals in this forum, Reddit, Steam forum, etc are having or had trouble with the black screen window on start-up of For Honor. From what I have read so far on how to fix this issue, the black screen bug, glitch, (just a pesky **** honestly) or whatever you want to call it has been an issue for multiple releases. Assassin's Creed, Myst, Riven are a few. When problems like this go unaddressed for so long, with an issue which seems to me can be easily resolved it says sooooo much about the brand. For Honor looks great! Hopefully, For Honor gets an awesome release with I hope minimal bugs, etc. Unfortunately, I will now wait for reviews to decide on this one. Thanks for hearing me out.
Black Screen on start up needs to be added to the list of "Known Issues" thread
It appears the black screen can be remedied by placing all the game files on the same drive as your OS.
For myself, this was somewhat annoying as I have a 250 GB SSD dedicated to my applications and OS and a 1TB SSD dedicated to my games and other storage.
I had to create an entirely new Steam Library on the C:\ drive for this game alone.