LONDON — Hillary Clinton got closer than any American woman to the nation’s top job, but her loss this week has thrown a spotlight back on the question: Why has the United States lagged behind so many countries around the world in choosing a female leader?

Tiny Sri Lanka became the first to shatter the political gender barrier more than a half-century ago, when that island nation was known as Ceylon. Its giant neighbor, India, followed a few years later. Since then women have attained top leadership posts — president, prime minister or its equivalent — in more than 70 countries in Europe, Latin America and the Asia-Pacific. Today, women run two of Europe’s most powerful nations, Angela Merkel in Germany and Theresa May in Britain. So why not the United States?

Historians have offered a range of reasons. Many of the earlier women’s pathways were eased because their husbands or fathers were autocratic or charismatic leaders first. Some were chosen via parliamentary deal-making, not direct elections. Others were tapped as temporary leaders. Some scholars say that European democracies may view women as more suited to high political office because their governments are known for generous social-welfare programs, something that seems maternal. In contrast, the president of the United States is primarily seen as commander in chief, which is a frame more difficult for women to fit into.

“America is still seen as the policeman of the world, the guardian of the world and we still have a very gendered version of what leadership means,” said Laura A. Liswood, secretary general of the United Nations Foundation’s Council of Women World Leaders, a network of current and former female prime ministers and presidents. “Not only do we have to be liked, we also have to be tough.”