De Gaulle vetoed the British application to join the European Economic Community (EEC) in 1963, famously uttering the single word ‘non’ into the television cameras at the critical moment, a statement used to sum up French opposition towards Britain for many years afterwards.[41] Macmillan said afterwards that he always believed that de Gaulle would prevent Britain joining, but thought he would do it quietly, behind the scenes. He later complained privately that “all our plans are in tatters”.[35]

American President John F. Kennedy urged de Gaulle to accept the United Kingdom in the EEC, stating that a Europe without Great Britain would create a situation in which the United States were bearing the enormous costs of Europe’s protection without any voice. Kennedy applied pressure to de Gaulle by threatening to withdraw American troops from European soil, but de Gaulle believed that the United States would lose the Cold War if they were to leave Europe.[42] It encouraged de Gaulle to see Great Britain as America’s “Trojan Horse”.[43]

https://en.wikipedia.org/wiki/Foreign_policy_of_Charles_de_Gaulle