De Valera's thinking on external association was influenced, during his tour of the United States in 1919–20, by the US Sugar Intervention in Cuba. In U.S media in February 1920 he compared the future relationship between Britain and Ireland with the Monroe Doctrine relationship between the U.S. and Cuba. Darragh Gannon suggests the mixed reception this "Cuban policy" received among Dáil members foreshadowed the Treaty split of 1921–2. Nicholas Mansergh traces the first reference to "external association" to 27 July 1921, preceding a proposal by de Valera on 10 August for a treaty of free association between the Irish Republic and Great Britain. De Valera told Mansergh in 1965 that the idea of external association came to him "one morning as he was tying his bootlaces", shortly after Jan Smuts' exploratory visit following the June 1921 ceasefire which ended the Anglo-Irish War (later called the Irish War of Independence). In September 1921, David Lloyd George, the UK prime minister, proposed negotiations into "how the association of Ireland with the community of nations known as the British Empire may best be reconciled with Irish national aspirations". De Valera accepted and explained his concept of external association to the plenipotentiaries sent to London. Their head, Arthur Griffith, later said de Valera told him the idea was to get out of the "straitjacket of the Republic" while "bringing Cathal along", referring to Cathal Brugha, the staunchest republican in the Dáil ministry.