Politics at heart of royal marriages past

For centuries members of England's royal family were strategically married off to European royals with the aim of cementing allegiances, mainly to help avoid war but also to reap economic benefits.

Love simply wasn't a factor.

"Through the medieval period, any time a country wanted an alliance with another they would offer a prince or princess as a way of symbolising or cementing the alliance," royal historian and author Dr Anna Whitelock told AAP.

"It was as important as any diplomatic treaty. You had to have a marriage."

And the younger a betrothal could be secured the better.

Back in 1518, King Henry VIII betrothed his two-year-old daughter, the future Queen Mary I, to Francois, the Dauphin of France, who was just a few months old.

The match was agreed after long-time enemies France and England signed a peace treaty.

While officials decided the betrothal would only be binding if the couple consented to it when they were older, the plan was dumped in 1521 when Henry decided it would be better for Mary to marry her cousin, Roman Emperor Charles V.

"That was pretty standard," said Dr Whitelock, author of Mary Tudor: England's First Queen.

"That's what you were for if you were a princess, you were there to be married off."

Mary ultimately ended up choosing her own husband when in 1554, a year after she took the throne, she wed Philip II of Spain.

Mary's mother, Spanish princess Catherine of Aragon, was also a toddler when she was betrothed to England's King Henry VII's son Prince Arthur in the late 1480s.

But while they married when she was 16 in 1501, he died five months later and she was betrothed to her husband's younger brother, who as Henry VIII became one of England's most famous kings.

Marrying your cousin was also common, with Queen Victoria's union with her first cousin Prince Albert of Saxe-Coburg and Gotha, one of the most famous examples.

However, their match was most definitely based on love, with the famously devoted couple producing nine children after they wed in 1840.

Likewise for Queen Elizabeth II who last year celebrated 70 years of marriage to her third cousin Philip, a prince of both Greece and Denmark.

But married life hasn't agreed with three of their four children.

Prince Charles famously divorced Diana, Princess of Wales in 1996 after their fairytale marriage imploded, while his younger sister Princess Anne divorced Captain Mark Phillips in 1992 after 19 years together.

Their younger brother Prince Andrew's decade-long marriage to Sarah Ferguson also collapsed in 1996 following a series of scandals that included the Duchess of York having her toes sucked by her financial advisor John Bryan.

For Prince Charles' eldest son Prince William, his marriage to a middle-class woman from middle England, Catherine Middleton, appears strong with the couple having recently welcomed the arrival of their third child, Prince Louis.

Like William, Prince Harry has chosen to marry a commoner, American actress Meghan Markle - something unthinkable hundreds of years ago.

"The thing people love about Harry and Meghan is that they seem very at ease with each other and they aren't shy about displaying their affection for each other and now that's very much part of what people want to see as part of an authentic royal match," Dr Whitelock said.

Harry's marriage to an bi-racial American divorcee is also being interpreted by some as a move by the royal family towards being more inclusive and diverse.

"But I think people need to be careful not to read into it that there's been a sort of massive shift in the British monarchy in what's now acceptable and permissible," Dr Whitelock said.

"I think if Harry had wanted to marry Meghan in his early 20s when he was seen as a tearaway prince it would have been a different question.

"But also it's because he's not going to inherit the throne, so it's less of a radical departure than people think."

What was way too radical was when the Queen's uncle King Edward VIII wanted to marry the twice-divorced American socialite Wallis Simpson.

Edward was forced to abdicate in 1936 because Church of England officials didn't want him to marry Mrs Simpson because her former two husbands were still alive.

The couple did marry a year later, by which time Edward's brother King George VI, the current Queen's father, was on the throne.

With that scandal long gone, Dr Whitelock believes the royal family is enjoying a bit of a renaissance.

And while Harry's union with Meghan is not one based on diplomacy, Dr Whitelock believes the couple could exert some "soft" political power, particularly in Commonwealth countries, which Harry has said he is keen to focus on.

"The kind of injection of energy and attention for the Commonwealth from Harry and Meghan is really smart and it gives them a role that's distinct from Kate and William," she said.

"So while it's not a political alliance as such, I think that they will be used in a kind of political with a small 'p' way if nothing else to sure up the position of the British monarchy."

Australian Associated Press