Who at fault on head on collision car accident?

In all crashes there is an underlying cause or driving error.

The person who made the error and presumably broke the law is at fault.

In virtually all head on crashes some one is on the wrong side of the road, from there we need to know why, if they justed oopsed, the person on the wrong side is at fault.

If there was another crash that forced the car into the wrong lane caused by a third car the third car would be at fault for the whole mess.

And so on.