Is static friction the only force causing a car to move (without sliding)? A car is moving without sliding means that the friction between wheels and the ground is static friction. This is the force causing an object to move forward, therefore, its direction is the same as the moving direction of the car.
My question is: For the horizontal forces acting on any moving(without sliding) car, $\ F_{fs}$ always oriented forward, what's the backward force to balance $\ F_{fs}$ so as to keep the car moving uniformly? Is that the Force produced by engines?
Just to clarify, I am referring to auto cars (with engines).
Any help or thoughts are appreciated!!!
 A: 
what's the backward force to balance $F_{fs}$ so as to keep the car moving uniformly? Is that the Force produced by engines?

The forwards force comes from the torque produced by the engine of the car and is transferred into the ground via static friction. The retarding force that keeps the car moving at the same speed is mostly air resistance (as well as a large assortment of inefficiencies in the actual mechanics of the car).
A: I agree that friction in the drive mechanism reduces thrust, rather than opposing the motion of the car. However, this is not the case for wheels which are not in the drivetrain - ie where there is front/rear wheel drive instead of 4-wheel drive. Friction in non-drivetrain wheel mechanisms are then sources of resistance to motion.  If the car has rear-wheel drive, then the static friction on the rear wheels is forwards and the friction on the front wheels is backwards.
In both types of wheel there is also "rolling resistance" which is the net horizontal component of mostly vertical forces caused by deformation of the tyre.
https://en.wikipedia.org/wiki/Rolling_resistance
A: A free body diagram will show a car in motion has air drag force, gravity force and friction force on it. The net force keeps the car accelerated, decelerated, or moving at constant speed. 
Friction force is due to relative motion between wheel and ground. Engine output spins the wheels (torque from power train system balances the torque produced from the frictional force).   
Air drag force is proportional to car velocity to the power 2. It works opposite to the car moving direction. Zero air drag occurs when car is in stall. On horizontal surface, this is the only force on the car external opposite to the frictional force. 
If the car is on slope, it can either move itself (down slope) or it need extra force from the frictional force.
There are many areas that consumes engine output such as frictions inside power delivery system and wheel sliding friction.  
