"Sovereignty no longer exclusively protects States from foreign interference; it is a charge of responsibility that holds States accountable for the welfare of their people.
Prevention requires apportioning responsibility to and promoting collaboration between concerned States and the international community. The duty to prevent and halt genocide and mass atrocities lies first and foremost with the State, but the international community has a role that cannot be blocked by the invocation of sovereignty. Sovereignty no longer exclusively protects States from foreign interference; it is a charge of responsibility where States are accountable for the welfare of their people. This principle is enshrined in article 1 of the Genocide Convention and embodied in the principle of “sovereignty as responsibility” and in the concept of the Responsibility to Protect." Quotation from web page of UN's Special Advisor on the Prevention of Genocide. (Viewed 15 April 2013)
Responsibility to Protect by 
The Responsibility to Prevent: overcoming the challenges of atrocity prevention by Printed resources
The subject search terms (below) should help you find more via SOLO
Intervention (international law)
Responsibility to protect (international law)
Humanitarian intervention
Humanitarian assistance
Atrocities - prevention
Crimes against humanity - prevention
Genocide intervention
Conflict management
Security, International
“Nothing contained in the present Charter shall authorize the United Nations to intervene in matters which are essentially within the domestic jurisdiction of any state”. Article 2.7 of UN Charter
Intervention by invitation
and
Intervention, prohibition of
two articles in MPEPIL see link below
Humanitarian Intervention and the Responsibility to Protect by 
Humanitarian Intervention : a history by 
Humanitarian Intervention by