SCOTLAND has a long military history, whether in its centuries of conflict with England, or later in its outsized contribution to the British Army.

It can even boast the oldest infantry regiment in the British Army, the Royal Scots, raised in 1633 and now part of the Royal Regiment of Scotland. But the Royal Scots were not originally created as part of the Scottish army.

Instead, they were founded to fight for France and her Protestant allies in the Thirty Years’ War, part of a long history of Scottish soldiers and mercenaries fighting abroad that stretches back to the Middle Ages.

Even since the Auld Alliance between Scotland and France began in the late 13th century, Scottish soldiers went to join the French army.

The Earl of Douglas and his cousin Archibald the Grim led a small Scottish contingent at the Battle of Poitiers in 1356, one of the key battles of the Hundred Years’ War between England and France. The battle ended in defeat and with the capture of both Archibald and the French king Jean II.

The largest Scottish contribution in the war came in between 1419 and 1424, when some 15,000 Scots went to France under the command of leading Scottish nobles such as John Stewart, earl of Buchan, and Archibald Douglas, earl of Douglas.

They had an early success in 1421 when, together with the French, they beat an English army at the Battle of Bauge. After arriving in France in 1424, Douglas was appointed lieutenant general of France and made Duke of Touraine by the French king Charles VII.

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Twin defeats followed at Cravant in 1423 and Verneuil the following year, which saw Douglas killed and destroyed most of the Scottish forces serving in France.

Some Scots even faced their own king on the other side of the battlefield. James I, an English captive since 1406, was brought to France by Henry V of England in 1420 to be used against the Scots fighting there.

The two kings were at the Siege of Melun that year. When the town eventually surrendered, the French garrison was taken prisoner, but the 20 Scots defenders were hanged as traitors for supposedly fighting against their king.

Henry V hoped that this would dissuade any more Scottish involvement in France. But Scottish troops continued to come. Between 1425-40, about 10-20% of French forces were Scots.

Most famously, from 1421 onwards, the French king selected some of the best Scottish soldiers to serve as his personal bodyguard, the Gardes Ecossaises, or Scots Guard.

Scots continued to join this elite unit of archers until well into the 17th century, after which its members were mostly French. Even so, the company retained many Scottish traditions, such as using Scots words for commands.

France was not the only country that welcomed Scottish soldiers. In the 16th and 17th centuries, Scots Presbyterians and Catholics would find themselves joining the Wars of Religion that raged across Europe.

In 1573, the Scottish government gave licences to three Scottish captains to raise 300 men each to go fight in the Netherlands. The Eighty Years’ War had broken out there a few years earlier, when the Protestant Dutch rebelled against their Catholic Spanish rulers.

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The Scots troops had little success initially. The Spanish were better trained and more organised.

Some Scots even defected to the Spanish side, which already had Scottish mercenaries of it own, often Catholics.

Many English Protestants also went to fight for the Dutch. Eventually, they joined together with the Scots fighting there in 1586 to form the Scots Brigade, after which the Scots began to excel, eventually making up a substantial part of the Dutch field armies.

Until the war’s end in 1648, about half of their infantry were Scots or English. For their successful defence of Nieuwpoort in the face of heavy losses in 1600, Frederick Henry, prince of Orange, called the Scots “the bulwark of the Republic”. The Scots Brigade would go on to serve in several other conflicts in the Netherlands, until the unit’s dissolution almost two centuries later in 1782.

But it was not until the most infamous of the Wars of Religion that Scottish mercenaries reached their height – the Thirty Years’ War from 1618 to 1648. This conflict, fought mostly in Germany but with the participation of almost every European power, saw tens of thousands of Scots fighting for both Protestant and Catholic rulers. It is estimated that around 50,000 Scots went to fight between 1625-42.

The beginning of the war saw Scots fighting in Bohemia, the modern Czech Republic, against the Austrian Habsburgs. There Colonel James Seaton’s regiment survived the collapse of its Bohemian allies, continuing to hold the town of Trebon for almost 18 months afterwards.

Other Scots fought with the French army, such as Sir James Hepburn’s regiment in 1633, a unit that would later become the Royal Scots.

But the vast majority of Scots ended up serving with another part of the anti-Habsburg alliance: the Swedes, who joined the war in 1630. Scots accounted for almost one-quarter of the Swedish field army in Germany and they also made up a substantial proportion of the Swedish officer class.

Between 1624-60, Sweden’s army included eight Scottish field marshals and generals, 69 colonels, and 49 lieutenant colonels. These Scottish troops were highly trained and capable, and played an important part in Sweden’s victory at the Battle of Breitenfeld in 1631.

Though it is Scotland’s military exploits within the UK that are often remembered today, its contribution to the Napoleonic Wars or the two world wars show the country had its own military tradition long before the 1707 Act of Union.

The reputation of Scottish soldiers as “sure men, hardy and resolute”, as one Englishman wrote following the siege of Bergen op Zoom in 1622, was built long before the United Kingdom even existed by tens of thousands of Scottish mercenaries serving in some of the fiercest wars of late medieval and early modern Europe.