how are horses supposed to birth naturally?

might be a dumb question, but i’ve been watching KVS for a while and i found myself wondering how horses are supposed to give birth without help.

Katie most of the times intervenes and i would be shocked to learn that if she does not, all the horses she did not help would be not alive if they were to birth in the wild.

my biggest thing is the sack breaking. how is supposed to break naturally? in many videos Katie “rips” it and then she says that the mares has 30 mins to push the baby out. if Katie were to not touch the sack how long would it take for it to naturally rip? and since the time limit, as far as i’ve understood, exists only once the sack is broken, is labour in general supposed to last longer if nobody intervenes?