After being in church and learning musical form, blacks began to develop their own style of music: Country/Texas Blues. This was the first time blacks had a music that was characteristic and unique to them.
There was almost always some sort of instrumentation, and the majority of the time the instrumentation was just guitar and voice.
The 12 bar blues form that we're familiar with today didn't really develop until years after Texas Blues became popular. Instead, Texas Blues forms were more free form because the melodies were more like solos and so the performer could take many liberties with the song, including length.
Perhaps the most popular Texas Blues guitarist was Robert Johnson (the man in the video). The reason he claimed to be so good at the Blues was because he had sold his soul to the devil in exchange to play the music well. Most importantly about Robert Johnson is that he's been credited for the invention of the turnaround. A turnaround consists of the chords in the last 2-4 measures of a song that lead the listener back to the first chord of the song. Sure, there were probably people who had done it before Robert Johnson, but he was the one to bring popularity to it. Fun fact: One of Eric Clapton's influences is Robert Johnson.
(I feel like I need a cool send-off phrase, like in Anchorman when they say "Stay Classy San Diego." I'm open for suggestions).
Note: I believe if "white" is politically correct, as is "black." I actually think "African American" is more offensive because it assumes the person is from Africa. If anyone can shed some knowledge I'm now aware of on this topic, please share.