If you were a royal in the late part of the 19th century, there’s a good chance you were related to Queen Victoria—and if Victoria was your grandmother, you were pretty much guaranteed a glamorous royal wedding to a prince or princess of her choosing.

“Victoria’s descendants effectively gained automatic entry into what amounted to the world’s most exclusive dating agency,” says Deborah Cadbury, author of Queen Victoria’s Matchmaking: The Royal Marriages That Shaped Europe. The outcomes of her grandchildren’s love lives were orchestrated by the queen herself, Cadbury says.

But those outcomes weren’t always happy—and by marrying off her grandchildren, Victoria inadvertently helped stoke a world war. Here’s how the queen’s matchmaking helped create—and destroy—modern Europe.

It wasn’t unusual for a monarch to be involved in her family’s marriages. The Royal Marriage Act of 1772 gave Britain’s monarch the chance to veto any match. But Victoria didn’t stop at just saying no. She thought that she could influence Europe by controlling who her family members married. “Each marriage was a form of soft power,” says Cadbury. Victoria wanted to spread stable constitutional monarchies like Britain’s throughout Europe.

Luckily, she had plenty of family members with which to do it. Victoria had nine children and 42 grandchildren. Eventually, seven of them sat on European thrones in Russia, Greece, Romania, Britain, Germany, Spain and Norway—and all would take sides during World War I with disastrous consequences.

Some of Victoria’s grandchildren followed their grandma’s orders without complaint. Her grandson Albert Victor was second in line for the throne and, at Victoria’s behest, asked Princess Mary of Teck to marry him. Victoria liked the German princess, who was also a cousin, because of her level-headedness, and pressured Albert to marry her even though he was rumored to be gay. He dutifully proposed. Then, tragedy struck and he died suddenly of influenza in 1892.

Victoria then pressured Albert’s brother, George, who was now second in line to the throne, to propose to Princess Mary. She accepted and, as queen consort of George V, became a beloved ruler.

But not everyone listened to their grandmother’s warnings. Victoria’s favorite granddaughter, Alix of Hesse, fell in love with Nicholas Romanov, heir apparent to the Russian throne. Victoria was horrified. She thought the Russians were barbaric and corrupt, and forbade the match. “Granny was right of course,” says Cadbury, “but Alix was in love.”

Though Alix turned down Nicholas twice, she eventually got Victoria’s grudging approval and married him right after he became Tsar of Russia. Their love was strong, but fated for tragedy: During Nicholas’ reign, Russia collapsed into revolution and war, and his British cousin, George V, declined to offer aid to the Romanovs, as he thought it would be politically unpalatable. The imperial family—Nicholas II, Czarina Alexandra and their five children—were executed by Bolshevik troops in 1918.

Once these first cousins took their thrones, they often found themselves at cross purposes. Victoria’s most contentious grandchild was Kaiser Wilhelm II, the volatile ruler of the German empire. He was the product of what Victoria once thought was one of her most successful matches: the marriage of her daughter, Vicky, to Prince William of Prussia. But unlike many of Victoria’s grandchildren, Wilhelm couldn’t be controlled by a word from his grandma.

As he veered closer and closer to war, says Cadbury, his mother Vicky “was driven almost to treason in her letters to her British mother, so alarmed was she by the actions of her son. ‘I think with fright and horror of the future’ she confided to her mother in 1897. ‘It makes one mad to think of all the misery that may yet come.’”

This misery crept across Europe as Victoria’s grandchildren, their spouses and their countries became more and more nationalistic and fragmented. As the balance of power in Europe threatened to break down, they took sides—sometimes against their own family members. George V opposed Kaiser Wilhelm’s policies (as did Czar Nicholas before his murder), and the diplomatic ties Victoria hoped she had helped form with her meddling matchmaking began to break down.

As the forces that would eventually cause World War I bore down on Victoria’s grandchildren, says Cadbury, the bonds of royal cousinhood became “essentially powerless.” The result was nothing short of tragic. “Cousin could betray cousin, husband was set against wife and even sister against sister,” says Cadbury.

The consequences were astonishing: World War I left more people dead than any war in history and left Europe in shambles. By then, Queen Victoria had been dead for 17 years, but the marriages she pushed for with such authority and optimism still reverberated through Europe.

As Victoria’s granddaughter, Victoria Melita of Saxe Coburg and Gotha wrote to her cousin, Marie of Romania in 1917, there was nothing to look forward to— “neither pride, nor hope, nor money, nor future.” For many of Victoria’s grandchildren, the war meant the end not just of their happiness, but their reigns: By the war’s end, the monarchies of Turkey, Austria-Hungary, Germany and Russia had fallen.

Today, Britain’s monarch exercises less power over royal marriages. Though the monarch must still give approval for royal weddings, sprawling royal dynasties are no longer engineered via matchmaking. But for many, says Cadbury, the idea of royal matchmaking feels like “the ultimate fairytale.”

The idea of a prince and princess finding true love may be the dream of many, but for many of Victoria’s grandchildren, what happened after the royal wedding was more like a nightmare.