Clinton has already made history by becoming the first female presidential nominee of a major US political party in her bid for the White House in November.
"This is historic, just as Barack Obama was historic. There is no question about that," said Ester R Fuchs, professor of public affairs and political science at Columbia University, referring to the first black US president.
Across the Atlantic, "Iron Lady" Margaret Thatcher broke the glass ceiling decades ago when she became British prime minister in 1979, and last month May did it again.
But these leaders remain in a minority and their numbers are only gradually increasing.
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A study by the Pew Research Center last year found women led only about 10 per cent of UN member states.
"Even while the number of female leaders has more than doubled since 2005, a woman in power is hardly the norm around the world," it said.
There are regional variations, with Finland, Norway and Iceland well used to female leadership, and South and Southeast Asia and South America performing better than elsewhere, according to UN Women, the United Nations body championing gender equality.
But it took until 2005 for Africa to have its first female elected leader, in Liberia's Ellen Johnson Sirleaf -- although the continent has a better record on ministers.
At the start of 2015, only 17.7 per cent of all government ministers in the world were female, but it was more than 30 per cent in Cape Verde, Rwanda and South Africa.
In Japan, Yuriko Koike last month became the first female governor of Tokyo, a rare breakthrough in a male-dominated society.
She has acknowledged it was a struggle to get where she is, once noting that Japan did not so much have a glass ceiling as a "sheet of steel" that women had to break through.
In Italy, another country where men still hold sway, Virginia Raggi and Chiara Appendino were elected this year as mayors of Rome and Turin respectively.
But Sofia Ventura, professor of political and social sciences at the University of Bologna, said their elections cannot yet be called a turning point.