together 1,900 guests, many of whom were pretty high profile people.

Footballer David Beckham was there with his wife and fashion designer Victoria Beckham.

Elton John was there too.

But this photo might be the most impressive of all, because

This is the Queen of Spain And the Prince of Spain

Next to the Princess of Sweden,

the former King of Greece is behind them,

And way back there is the former King of Romania.

They were invited because they're all related to Prince William's great-great-great Grandmother,

Queen Victoria.

Over the course of her 63-year reign, she strategically planned marriages to place her

descendants in royal families all over Europe.

And in doing so, created one of the most remarkable royal families in history.

By the early 19th century, Europe had been at war for decades.

After the French Revolutionary and Napoleonic wars killed millions, European leaders came

together to restore peace by reshaping major states for a new balance of power.

Great Britain went on to become one of the strongest states.

And years later, Queen Victoria and her husband Albert came up with a plan to maintain that

political power: They married their children to monarchs across Europe.

And at that time, you know,

all royal marriages were fundamentally about dynastic unions, about

cementing political allegiances, about building new political alliances.

It started with their daughter Vicky, the eldest of nine children.

She married the heir to the Prussian throne, the largest and most powerful of the German states.

Albert's vision had always been, and Victoria shared it,

that Prussia of all the German

states was the one that would end up leading the way towards a great unified Germany.

They wanted to build strong connections with Germany and see them as being a force for

good and constitutional benign monarchy across Europe.

Their children Alice, Beatrice, Helena, Leopold, and Arthur also married German royalty.

Their eldest son, Prince Albert Edward married a Danish princess whose brother was King of

Greece; two more important European states.

But when their son Alfred wanted to marry the daughter of the Russian Tsar, things became

a bit more complicated:

There was a long history about Queen Victoria's deep, deep apprehensions about

Russia, for any of her children marrying into Russia.

Well, the Russian monarchy was an autocracy,

whereas the British monarchy as such was a constitutional monarchy.

There was a whole long period of Russophobia in Britain.

The two states were also extremely competitive over territory in Central Asia and Eastern Europe,

where they fought a bloody war in the 1850s.

But the marriage was allowed and by the 1880s Queen Victoria's children were in several

important branches of Europe's monarchies.

But did that bring peace to Europe?

Not quite.

See, Germany did unify in 1871, but it wasn't peaceful.

Prussia fought a series of bloody wars and consolidated the other German states.

In Russia, the royal Romanov family was losing its grip on power.

Members of the monarchy were being hunted and the Tsar was assassinated in 1881.

The royal unions didn't play out as Queen Victoria planned, but she continued to make

more matches anyway.

She had 42 grandchildren in total,

and these 7 ended up on royal thrones.

The eldest, Wilhelm II, who was already in line to be the next Emperor of Germany, married

a German princess in 1881.

The hope was that he would steer a unified and powerful Germany

into an alliance with Great Britain.

George was in line to be the King of Great Britain and married a minor British royal

family member.

Alexandra married Nicholas, who was related to George and Wilhelm, and both became the

Tsar and Tsarina of Russia.

And four more granddaughters married European royalty, fulfilling Victoria's vision.

I mean, when you look at Queen Victoria by the end of her life

she really was the grandmother of Europe.

Take for example this family photo, where Queen Victoria is with her daughter and grandson,

the rulers of Germany.

Her son, Britain's next king, and her granddaughters, the future

Tsarina of Russia and future Queen of Romania.

Here's the soon-to-be King of England and his look-alike cousin the soon-to-be Tsar

of Russia.

And here's some of the children and grandchildren together.

Finally, this is King Edward of Great Britain and his nephew Kaiser Wilhelm of Germany

at Queen Victoria's funeral in 1901.

After her death, the family ties that Queen Victoria had strung around Europe, would not

bring peace, but the most destructive war Europe had ever seen.

The Kaiser, the king of Gothenberg,

make ready to sweep the field.

The Tsar of Russia mobilizes.

England joins the battle royale.

World War One broke out in 1914 and split this family apart.

Wilhelm's Germany along with Austria-Hungary and the Ottoman Empire, fought an alliance

led by Britain, Russia and France.

These countries were neutral.

Say Victoria had lived 'til we were on the brink of war.

I think it would have broken her,

totally broken her heart,

to know that her grandchildren ended

up at war with each other.

The war killed over 10 million people and ended the era of monarchy in Europe.

Wilhelm, Sophia, and Marie were all forced to abandon their thrones.

Revolution swept through Russia and Alexandria and Nicholas were executed by Communists.

The British monarchy survived, but the war forced them to rethink their political strategy.

George, King George V, and his wife Queen Mary were very very astute.

They saw that the monarchy had to be more people friendly, had to be more accessible,

not just sitting there in great robes in glory.

You know, with their crowns on. Had to be much

more out on the street, hands-on, meet the people, win their confidence.

The kind of monarchy we now have with Queen Elizabeth.

That approach not only helped modernize British monarchy over the last century,

but it also

changed the face of royal weddings, forever.