Sounds like your car's rear wheels are locking up on braking. Two things could cause that to happen: 1) Either the new rear brakes are too tight, or 2) The front brakes are not getting enough brake pressure. Almost every car on the road today has a dual circuit brakes, i.e. the rear brakes are separate from the front ones. If there's air in the front brake circuit and the rear brakes are doing most of the braking, the car will spin.
To keep troubleshooting this as simple as possible, start with the things you changed most recently. Why did you change the brake master cylinder? Have it bled again at all four wheels to remove any trapped air. Also jack up the rear wheels with the parking brake off (make sure front wheels are chocked) and make sure the wheels spin freely with just a hint of drag from the brakes. The wheel should spin between 1/2 to full turn. If it spins less than 1/2 a turn, the brakes are too tight and they need to be backed off a bit.
Next up, check all the lines and connections. If you have a weak rubber line that is expanding under braking pressure, it will let you know with a tug on the steering wheel to one side. Suspension issues can also cause a vehicle to spin but that is most likely not your problem.