The Prime Directive will state that the US will not interfere with other countries unless one of 3 conditions is met.
1. If that nation attacks us
2. If the people request aid (in cases of natural or man made disasters)
3. The other members of the UN security counsel agree to proposed action
We are not the police of the world nor are we some kind of moral leaders of it. We must avoid getting involved and this rule would help enforce it.