King George's War (1744 to 1748) was the third great colonial conflict fought in North America between Great Britain and France, each side aided by their respective Native American allies. Like the previous two major colonial wars, it coincided with a larger European conflict – the War of the Austrian Succession (1740 to 1748) – though it had its own origins unique to the political turmoil of Colonial America.

The war was rooted in the Treaty of Utrecht (1713), in which France had been forced to cede its colony of Acadia (Nova Scotia) to Britain. Fearful of losing the rest of their Canadian colonies, the French constructed the mighty fortress of Louisbourg on Cape Breton Island to protect their North American interests and check British expansionism. By the 1740s, Louisbourg was not only the most formidable European-built fortress in North America but also a bustling commercial town.

In 1744, war broke out between Britain and France; as in the previous two wars, the North American theater was named for the British monarch, in this case King George II of Great Britain (reign 1727 to 1760). Britain's New England colonies used the war as an excuse to remove the threat of Louisbourg and launched a military expedition against it. The Siege of Louisbourg of 1745 was a great victory for the New Englanders and, though it marked the climax of the war, fighting also took place across New France, New York, and New England.

In 1748, the Treaty of Aix-la-Chapelle ended the conflict, stipulating that Britain must return Louisbourg to France. The war helped unify the British colonists by giving them a common purpose and helped set the stage for the fourth, and final, great colonial war, the French and Indian War (1754 to 1763).

Over 30 years had elapsed since the Treaty of Utrecht had put an end to Queen Anne's War (1702 to 1713), the second great struggle between the colonial empires of Britain and France for control of North America. That war – characterized by a cycle of murderous retaliatory raids in the northeast and failed military expeditions into Canada – had ended with the British seizing control of Acadia, a former French colony that the victors promptly renamed Nova Scotia.

The loss of Acadia put the other colonies of New France in a precarious position, as the British were now situated threateningly on their doorstep. So, in 1718, the French began construction of a fortress on Île-Royale (Cape Breton Island) to offset the British influence in the region. This fortress was built with the goal of defending the vital supply line up the St. Lawrence River to Quebec and protecting the profitable French fisheries off the coasts of Nova Scotia and Newfoundland. By the early 1740s, this fortress had transformed into a mighty citadel that the French named Louisbourg in honor of their late monarch, King Louis XIV of France (reign 1643 to 1715).

By 1740, Louisbourg had become one of the largest and most formidable fortresses built by Europeans in North America, earning it the nickname ‘the Gibraltar of the West'. It included 2.5 miles (4 km) of stone walls, which in some places measured 30 feet (9 m) in height and 36 feet (11 m) across. Ditches and ramparts added further protection, as did six great bastions, situated at various points. The fortress had enough embrasures to mount 148 cannons – though historians estimate it had no more than 100 guns mounted at any given time – and enough barracks to house a garrison of 1,500 soldiers.

The fortress had been monstrously expensive and had cost an estimated 3.5 million livres to construct. This was four times the annual budget usually spent on all New France combined, causing King Louis XV of France (reign 1715 to 1774) to joke that, for that cost, he should be able to see the tops of the fortress's walls all the way from Versailles. This expense, however, could be expected to be partially recouped by Louisbourg itself since, in addition to being a mighty fort, it was also a bustling commercial town. Within its mighty walls, 4,300 French colonists lived and worked, exporting products made from fish. By the 1740s, Louisbourg had become France's second most important city in the New World after Quebec itself and had become the third largest port in all North America (after Boston and Philadelphia).

Louisbourg's very existence, therefore, was seen as a threat to British North America, particularly the nearby New England colonies. But despite these simmering tensions, the shattering of the 30-year peace would not take place along the Canadian border, but in the West Indies. Viewing the Spanish Empire as a power in decline, Britain had declared war in 1739 on the pretext that Spanish coast guards had mistreated and mutilated an English sea captain, Robert Jenkins, whose ear had been sliced off.

British Vice Admiral Edward Vernon then led a squadron of British warships into the West Indies, scoring a series of small victories against Spanish ports. The goal, aside from simply increasing British control over the lucrative West Indies, was to send a threatening message to Spain's ally, France, that Britain was still the master of the Americas. But the tables turned in 1741, when Vernon's massive invasion force met with destruction at the Battle of Cartagena de Indias; devastated by tropical diseases, Vernon's men died by the thousands and were forced to turn back.

The so-called War of Jenkins' Ear (1739 to 1748), rather than showcasing British power, simply proved to the French that British expansionism had to be stopped in order to protect their own imperial interests. The stage was set for yet another clash between the great colonial empires of Britain and France.

By the time that Vernon's fleet met with disaster outside the walls of Cartagena de Indias, the entire world had gotten swept up in war. In Europe, disputes over the succession of Empress Maria Theresa (reign 1740 to 1780) to the Habsburg throne had led to the War of the Austrian Succession – as usual, the war pitted Britain against France, an imperial struggle that would soon spread to their colonies. It was not until March 1744, however, that war between the two powers was formally declared.

News reached Louisbourg on 3 May 1744, and the French soldiers there quickly mobilized, intending to strike first. On 23 May, the French and their Indigenous allies from the Mi'kmaq and Maliseet nations raided the British fishing post of Canso in Nova Scotia. Throughout the month, they mounted additional raids on British fisheries while French privateers targeted New England shipping. In July, Father Jean-Louis le Loutre, a French missionary priest, raised a force of Mi'kmaq and Maliseet warriors to assault Annapolis Royal, the British capital of Nova Scotia. Also included in Loutre's force were Acadians, descendants of the original French settlers of Acadia who sought to return their homeland to French control.

When Loutre's force arrived outside Fort Anne – the fortress defending Annapolis Royal's harbor – they found it better fortified than expected. The British, jolted into action by the recent raids in Nova Scotia, had spent the previous few weeks readying themselves, strengthening Fort Anne's walls and bolstering its garrison. After a short siege that lasted a meagre few weeks, Loutre realized he did not have the siege equipment necessary to scale the fort's walls and withdrew.

On 9 September, another, larger French and Mi'kmaq force arrived and began to lay siege. Each night, the Mi'kmaq warriors would taunt the defenders outside their walls, hoping to lower their morale or draw them out into a battle. But the British continued to hold out.

On 26 September, the British were reinforced by a New Englander, John Gorham, and his company of rangers. Gorham's rangers were among the most experienced and most formidable ranger units in Colonial America, and were quick to set about their grisly work. One night, they launched a surprise attack against one of the Mi'kmaq encampments, killing men, women, and children, and mutilating their bodies. The next morning, the Mi'kmaq quit the siege, depriving the French of most of their manpower. By 5 October, the French themselves were forced to retreat, leaving Fort Anne – and Annapolis Royal itself – still flying the British flag.

In January 1745, Governor William Shirley of the Massachusetts Bay Colony appeared before the Massachusetts legislature with a daring proposal – an attack on the Fortress of Louisbourg. He had received intelligence that the mighty fortress was less impregnable than was initially believed, and that the garrison was small and malcontent. Moreover, he knew that the New England colonies had to free themselves from beneath Louisbourg's monstrous shadow and that they needed to try to attack it, with or without aid from the British Army. The legislature narrowly voted to support Shirley's proposal – but only after extensive lobbying from Boston's merchants, who had much to gain by the neutralization of Louisbourg's harbor.

Having secured his own colony's stamp of approval, Shirley approached his fellow colonial governors to ask for their support for the expedition. The colonies of Connecticut, New Hampshire, New York, Rhode Island, Pennsylvania, and New Jersey each pledged military support, either in the form of troops or funds. Shirley also managed to convince Commodore Peter Warren, commander of a squadron of British warships in the West Indies, to join the expedition.

On 4 April 1745, the colonial expedition set sail from Boston. Under the command of Lieutenant General William Pepperell, a 49-year-old native of Maine, it included some 4,200 soldiers aboard 90 ships. The expedition briefly stopped at Canso, Nova Scotia, to resupply and wait for the snows to thaw before continuing on to Louisbourg, burning the small French fishing communities that lay in their path.

On 11 May, a detachment of the provincial troops established a beachhead on Cape Breton Island and, after a brief skirmish, chased away the French and Indigenous troops that had sallied out to contest them. Pepperell spent the rest of the evening landing his men and setting up camp, while Commodore Warren's Royal Navy ships set up a blockade of Louisbourg's harbor. The path to Louisbourg was defended by two French batteries, Royal Battery and Island Battery. The cannoneers of Royal Battery, however, grew terrified by the mass of colonial troops assembling onshore and deserted their posts without a fight, failing to even spike the cannons. Island Battery would hold out for weeks, repelling several assaults made by the New Englanders. But the provincials set up batteries of their own and, at the end of May, managed to pound Island Battery into submission.

Having taken the two outlying French batteries, it was time for the provincials to turn their guns on Louisbourg itself. The provincial cannons and the captured guns roared to life, spewing fire and lead into Louisbourg both day and night. "Never was a place so badly mauled with cannon and shells," Pepperell would report after the siege (quoted in Baker, 31). By Pepperell's own estimate, the provincials fired some 9,000 cannonballs and over 600 mortar bombs into the town during the siege. The damage was catastrophic. Streets were pockmarked with craters, entire buildings leveled, the fortress' once mighty bastions reduced to rubble.

Naturally, this put great pressure on the French soldiers – those who did not desert were forced to live under the hellish conditions of projectiles constantly soaring overhead and exploding around them. By 27 June, the French had had enough. After news reached them that the expected reinforcements were not forthcoming, the commander capitulated, and Pepperell's victorious troops entered the once impregnable fortress. It was a stunning success – a strong European fortress, manned by well-trained regular soldiers, taken by a hodgepodge of backwoods colonial troops. The Siege of Louisbourg marked a turning point, not only in the war but also in the story of the American colonists, who thereafter felt a sense of unity that would only grow stronger in the decades to come.

The French were not about to take the fall of Louisbourg lying down. In early 1746, they began preparing a military expedition of their own to recover the fortress, which would include 11,000 men and 64 ships under the command of the Duc d'Anville. This mighty force set sail from France in June 1746 but quickly met with disaster. First, it got caught in a storm in the Bay of Biscay, damaging the ships and slowing progress. Then, deadly diseases such as typhus and scurvy broke out, killing or incapacitating hundreds of sailors and soldiers.

Just when it seemed the expedition could not get any unluckier, one of the ships was struck by lightning, causing a magazine to explode and kill or wound 30 men. In late September, the expedition finally reached Nova Scotia after nearly three months at sea. But no sooner had they arrived than d'Anville suffered a stroke and died. The man who replaced him as commander of the expedition suffered a nervous breakdown and resigned after a failed suicide attempt. Despite this lack of leadership, the French soldiers marched off to attack Annapolis Royal. They never made it. Disease continued to decimate their ranks and soon forced them to turn around. Thus, by the end of October, the expedition was called off – a bitter and disastrous failure.

In the meantime, New France and its Indigenous allies continued raiding British settlements. On 28 November 1745, 600 French troops and Indigenous warriors raided the town of Saratoga, New York, burning it and killing or capturing over 100 of its residents. The raid had its desired effect and sent waves of panic throughout the frontier settlements of New York and New England; the British colonists abandoned every town north of Albany, New York, to avoid falling victim to future raids.

In June 1746, Sir William Johnson, an Irish-born liaison between New York and the Iroquois Confederacy, approached the Iroquois to convince them to join the war against the French. The Iroquois had previously formed an alliance with the English in New York, a pact known as the Covenant Chain, but were now resistant to Johnson's attempts to invoke it. At the end of King William's War (1688 to 1697), the English had signed a separate peace with the French and had essentially abandoned the Iroquois to keep fighting by themselves. Feeling betrayed, most of the Iroquois now remained skeptical of trusting the English. Johnson managed to convince the Mohawks, the most Anglophile of the Six Nations, to join him, but the others remained uncommitted and sat out the war.

After d'Anville's failed expedition, fighting in North America was mainly relegated to small skirmishes and retaliatory raids. Then, in October 1748, the great European powers signed the Treaty of Aix-la-Chapelle, ending the War of the Austrian Succession and all its related conflicts. The treaty stipulated that Britain had to give Louisbourg back to France in exchange for the city of Madras in India. The New Englanders were incensed by this. After all, they had captured Louisbourg with their own sweat and blood and saw no reason why it should be returned to the French. The British Crown was not unsympathetic to the New Englanders' plight, however, and paid Massachusetts £180,000 for its troubles.

The war had certainly taken its toll on the colonies – by some estimates, Massachusetts had lost 8% of its male population of fighting age – but the feeling that it had all been for nothing caused resentment to simmer between the British and French colonists. These tensions would boil over one final time in the last great struggle between Britain and France over control of North America: the French and Indian War.