Basically for back end development, you need to become good a language that can be used on the backend (python, go, javascript (through node.js, ect ect), and then learn sql and a database (such as mysql or postgress).
React is a javascript library made by facebook that's used for the front end, if you're focusing on the backend then I wouldn't worry about it. Javascript is pretty much the only programming language (html and css are also used but they aren't programming languages) used on the front end so you're forced to learn javascript well if you want to do front end development or fullstack development (this is front + back doing the fusion dance form DBZ).
im the opposite of you, i'm focusing on learning front end, so focusing on html5, css3, flexbox, css grid, bootstrap, react, redux and vanilla javascript. once i feel comfortable with all of that, i will attempt to learn the backend.
as for node.js, it's a javascript runtime that lets you use javascript on the backend (since it was originally front end only), which lets you use javascript on both the front and back end.
but yeah if you're focusing on the back end, stick with python, its an amazing language and django is a great framework, and then learn about the front end once you feel comfortable with python, django, sql, databeses, and api