Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
You've got your answer. The missing word is 'hence'.
Do you understand the word "hence"?
not a teacher
But I don't quite get it, can you rewrite the sentence?
Afghanistan has no formal party or primary system, hence the large field.
Afghanistan has no formal party or primary system, that's the reason for there being so many candidates.
I've always thought that thence made more sense than hense in this type of context.