According to journalist Samantha Power, the author of "", Zimmermann’s career in Yugoslavia was marked by "frustration with the resistance of the Bush administration to intervene". His last official act before he was recalled to the United States on 16 May 1992, was to write a confidential memo called "Who Killed Yugoslavia?" to the secretary of state. Each of the five sections of the memo was headed by a verse from the poem "Who Killed Cock Robin?". In Zimmermann's analysis, the nationalism of the Balkan leaders had led to the demise of the country.