Little more than a year after winning what many thought was an unwinnable electoral mandate, David Cameron was swept out of power on that continual bugbear of the Conservative Party - Britain's relationship with Europe. Cameron was certainly not the first Conservative Prime Minister to fall on an issue of Foreign Policy. Theresa May should be wary because it is highly unlikely he will be the last.
The Conservative Party has had a long love-hate relationship with Europe. Naturally wary of political integration, many Conservative backbenchers are nonetheless strong supporters of the concept of European defence as enshrined in NATO. Many in the party would describe themselves as more 'Atlanticist' than 'European'.
Winston Churchill developed a model, still familiar today, of the UK sitting at the heart of the American, European and Commonwealth spheres of interest. But this did not provide him with any guarantees of success in the vexed issue of foreign affairs. His second premiership from 1951 to 1955 was marked by the decline of Britain as an imperial power, military action in Kenya and Malaya and tense Anglo-US disagreements about European defence magnified when the US refused to prop up Britain's degenerating Imperial position in Egypt. Churchill added the Foreign Office to his portfolio in 1953 and the pressure probably contributed to his stroke of that year. Following his recovery, but with his power waning, the last 18 months of Churchill's time in office were marked by further disputes over how to deal with the Soviet threat and the very nature of transatlantic politics with the USA.
Churchill resigned in 1955 and his successor, Anthony Eden, is best remembered for the disastrous, at least in political terms, Anglo-French invasion of Suez in 1956. Eden's failure to garner sufficient US support ensured that a successful military operation did not result in a successful political outcome for Britain. The debacle highlighted Britain's decline as a key global power, undermined his position in the Conservative party and led to his resignation from office in January 1957.
Eden's successor Harold Macmillan continued to oversee the process of decolonisation but his premiership was rocked by the Profumo affair of 1963. That same year General De Gaulle blocked Britain joining the EEC. The lingering scent of scandal and ineffective European policy infused Macmillan's successor Alec Douglas-Home's year long period in office, which ended in October 1964.
The Tories were not in power again until 1970 under Edward Heath. He supported the US bombing of Hanoi, and his ministry oversaw the escalation of trouble in Northern Ireland including Bloody Sunday and the introduction of Internment. Nevertheless, he delivered a success: Britain's first foray into the Europe community with the European Communities Act. Heath's government is often associated with rising unemployment, labour disputes, power cuts and the Three Day week. But UK domestic problems were in part associated with insecurity in the Middle East, most importantly the 1973 Arab-Israeli War and resulting Oil Embargo. That allowed domestic pressure from miners strikes to create the discontent, which undermined Heath's leadership and led to the coronation of Margaret Thatcher.
The leadership of the longest serving Prime Minister of the Twentieth Century benefitted from an existential threat, in the form of the Soviet Union, and the visible support of an ally, President Ronald Reagan. Both defined Thatcher's premiership at home and abroad. But by 1990 the Soviet Union was imploding. Without the Cold War she looked suddenly obsolete and her influential international supporter had also gone. Without those two pillars she could no longer command authority at home. Again it was disputes over Britain joining the European Exchange Rate Mechanism (ERM) that caused her Deputy PM, Geoffrey Howe, to resign prompting a process that would culminate in her resignation in November 1990.
Her successor, John Major, won a mandate to govern in the 1992 election, but with a Commons majority of just 21, which made his leadership vulnerable to conflicting voices within the party. The Major government was blighted by Black Wednesday (16 September 1992), when the UK government spent around £3.3 billion in a futile attempt to prop up sterling, leading to the withdrawal from the ERM. That undermined credibility with the country, an impression fuelled by party in-fighting over Maastricht and the sniping of the Eurosceptic 'bastards'. The conditions were set for the rise of New Labour and Tony Blair.
The lessons of history are clear. When Labour Prime Ministers have been forced out of office or lost elections, it has often been over poor economic performance rather than because of foreign affairs. Conservative Prime Ministers are brought down by both the general deterioration of foreign conditions, 'things happening' overseas, which influence the domestic situation, such as the 1973 Oil Embargo and its effect on Heath's premiership, or political and strategic blunders, such as Suez and Brexit. Both were self-inflicted fatal wounds to Eden and Cameron.
Conservative Prime Ministers are brought down by Foreign policy issues, more often than not, over the issue of Britain's relationship with Europe. Brexit brought Mrs May to the Premiership; delivering it could take it away from her.