I have more or less the same feelings as the OP and yeah, there is barely any explanation on what’s going on politics wise etc. I had no idea where the First Order came from or why the New Republic and the Resistance weren’t part of the same team.
The lack of political context irked me at first. Eventually, I realized the relationship between the Republic and the Resistance is at least roughly analogous to the relationship between the French Resistance and Free France in World War II. This is an imperfect analogy but the closest historical example I can think of at the moment.
The Republic and the First Order each occupied a large part of the galaxy. Wary of an arms race out of a fear it could provoke war, the Republic signed a disarmament treaty with the First Order, which reneged on the agreement. The Republic secretly provided indirect support to the Resistance while publically denying this.