The course of history might have been very different if some of the world's past leaders and dictators had seen a psychiatrists, according to doctors.
Dementia may explain Stalin's behaviour
Consultant psychiatrist Dr George El-Nimr said World War II might not have happened if past US president Woodrow Wilson had bowed down to his dementia.
Stalin and Franklin D Roosevelt most probably had dementia too, he said.
Dr El-Nimr and colleagues spoke at the Royal College of Psychiatrists' annual conference in Harrogate.
Dr El-Nimr, from Haywood Hospital in Stoke-on-Trent, and his colleagues Dr Baseem Habeeb, at Mersey NHS Trust, and Dr Emad Sulib, senior lecturer in psychiatry at Liverpool University, looked at the possible impact dementia may have had on seven world leaders.
Millions of Russians might have been saved from death if the dictator Stalin had seen a psychiatrist, they believe.
They told doctors attending the conference that Stalin's behaviour could easily be explained by dementia following a series of strokes.
"This might be an explanation for the florid paranoia, dimming of superior intellect and the unleashing of his most sadistic personality traits," said Dr El-Nimr.
He said Franklin D Roosevelt's dementia might have impaired negotiations with Stalin at Yalta at the end of World War II in 1945.
Peace not war
World War II might never have happened if the US president around the time of the end of World War I, Woodrow Wilson, had stepped down after developing dementia, the researchers suggest.
It might then have been possible to persuade Congress to ratify the Versailles Treaty, which, in turn, would have led to the US embracing the League of Nations and possibly have averted the war, they said.
Dr El-Nimr said the British Prime Minister Harold Wilson as an example of the best case scenario.
The shock resignation of Harold Wilson in 1976 was down to his "remarkable awareness" a year earlier of his cognitive deterioration, said Dr El-Nimr.
According to the researchers, other leaders who developed dementia include Urho Kekkonen of Finland and British Prime Minister Ramsay MacDonald.
"It was obvious that some had what we call dementia," said Dr El-Nirm.
"It's not only to do with memory, it is to do with things like decision making, prioritising and sense of direction as well.
"If these have been affected this can obviously effect people's decisions, even in the early stages of dementia," he said.
He said people with high intellectual function before they get dementia might function well for longer and people might not notice, but their condition would still affect their performance at work.
"Early detection and treatment of this could have benefited the future of those countries and even the world," he said.