Why are rebels on the march in CAR

Who’s in charge in the Central African Republic (CAR)? It depends on who you ask.
Rebel forces are now in control of two thirds of the country, but they’re not quite done yet. They want to see President Faustin Archange Touadéra gone.
He was re-elected last December, but his opponents say he didn’t win fair and square.
Rebels have encircled the capital, Bangui, but the city is being guarded by government forces backed by UN, Russian, and Rwandan troops.
Meanwhile, thousands of people have fled the country fearing for their safety.
So, how did we get here? And where did this rebellion begin?