Original: He earned a high international profile when, in the aftermath of the killing of thirteen unarmed civilians in Derry by British Paratroopers (known as "Bloody Sunday"), he travelled to the United Nations in New York to demand UN involvement in peace-keeping on the streets of Northern Ireland.
Simplified: After "Bloody Sunday"), he travelled to the United Nations in New York to demand UN involvement in peace-keeping on the streets of Northern Ireland.