What If . . . Little Prince Hal had lived

Amid the fascination with anniversaries, one historic date has gone oddly unnoticed. It is almost exactly 500 years since the birth of one of the most important kings in our history, who transformed the appearance and culture of early-modern England.

Born on New Year's Day 1511, Henry of Cornwall, as he was originally known, was the long-anticipated son and heir to Henry VIII. After barely two months, the "New Year's Boy" was struck down by a mysterious illness and almost died. But he pulled through, and English history was never the same again.

At his father's court, little Hal was the star of the show, his father's darling who could do no wrong. His birth consolidated the passionate relationship between Henry VIII and his wife, Catherine of Aragon; indeed, after his baby son's brush with death, Henry was even more strongly influenced by his wife's Catholic piety. Ten years later, when he wrote his Defence of the Seven Sacraments, attacking Martin Luther, Henry dedicated it to his young son. "A gift from God," he wrote, "and a sign of divine love for our beloved country."

Little wonder that Henry VIII is remembered today as such a staunch defender of the Catholic Church; little wonder, either, that his regime was so assiduous in rooting out Protestant dissent.

At Henry's death in 1547, his son took over as Henry IX. At 36, Prince Hal was at his physical and mental peak. Tall and handsome, with his father's red hair and mother's fine features, he seemed the very model of a Renaissance prince.

Like his father, he had an eye for the ladies, even though his young wife, Katherine Howard, had already borne him two sons. And like his father, he was a ferociously loyal Catholic. Five years into his reign, exasperated by the spread of Protestant ideas in wealthy trading towns, he invited the Inquisition into England to root them out.

Although some historians describe Henry IX's rule as a reign of terror, most still see it as England's golden age. Once Protestantism was driven underground, the dynamic new king began to turn England into the great bulwark of the Counter-Reformation. Church music became ever more elaborate; art and architecture became ostentatiously spiritual. Henry threw men and money into the Continental struggle for Catholic supremacy, smashing Protestant rebellion in Spain's Dutch possessions.

By the time he was succeeded by his equally fervent son Henry X in 1577, England's position at the head of the Catholic world was assured. And even today, we owe many of our social conventions – the taboos on homosexuality, birth control and abortion, our fondness for large families, the Church's dominant role in education – to Hal's 30-year reign.

Dominic Sandbrook is a historian and author. His books include Never Had It So Good: A History of Britain from Suez to the Beatles and White Heat: A History of Britain in the Swinging Sixties. He writes the What If... column for the New Statesman.