The War of Jenkins' Ear (1739 to 1748) was a colonial conflict fought between Great Britain and Spain, primarily in the Caribbean and off the coast of South America. Looking to protect its interests in the West Indies, Britain provoked a war with Spain, one of its biggest colonial rivals, citing the mistreatment of one Captain Robert Jenkins, who was detained – and allegedly mutilated – by Spanish coast guards as they searched his ship for smuggled goods. In 1739, British Vice Admiral Edward Vernon sailed a fleet into the Caribbean, where he won some victories before his eventual defeat at the Battle of Cartagena de Indias in 1741. After that climactic battle, the war fizzled out as the British soon had their hands full with other conflicts, such as the War of the Austrian Succession (1740 to 1748) in Europe and King George's War (1744 to 1748) in North America.

Since the conclusion of Queen Anne's War (1702 to 1713), the European colonial powers in North America had enjoyed a relative period of peace. This was largely the work of Sir Robert Walpole, the leading British politician of the day, who became prime minister in 1721. Walpole and his Whig government believed that the British Empire would profit more from avoiding wars, both on the continent and overseas. Without the burdensome cost of military upkeep, Walpole was able to lower taxes while simultaneously working to pay off the national debt, with a sinking fund. Though many celebrated this pacifist policy, it was opposed by the Tories in Parliament, who feared that a non-combative Britain would soon fall behind its rivals, particularly in the Americas. The French, for example, were steadily expanding their influence in the West Indies, growing rich off their sugar plantations there. Should French meddling in the region go unopposed, then France would surely dominate the lucrative West Indies trade, at the expense of Britain's imperial interests. For these reasons, the Tories demanded a show of military force before it was too late.

But even the hawkish Tories were aware that a direct war with France could lead to a long and costly struggle. Instead, they decided to assert their influence in the West Indies by picking on another target they deemed to be weaker: Spain. For centuries, the Spanish had dominated commerce in the West Indies with a trade network connected by four major ports: Veracruz, Portobelo, Cartagena de Indias, and Havana. But Spain's overseas empire was not as powerful as it once was and was viewed by the British as bloated, decadent, and ripe for the taking. Britain's hostility towards Spain was also fueled by an anti-Catholic, anti-Spanish stereotype called the 'Black Legend', in which Spaniards were painted as cruel and greedy brutes. For these reasons, the Tories clamored for a war with Spain, both to assert British dominance in the West Indies and to send a message to France by beating up its weaker ally. The Spanish, for their part, were not blind to Britain's expansionist desires and spent the period of peace watching the other colonial power with unease. Their suspicions seemed confirmed when, in 1732, the British founded a new colony, Georgia, right on the doorstep of Spanish Florida, increasing tensions on the mainland as well.

Amidst all these rising tensions, Britain and Spain continued to trade in the West Indies. However, Spanish ports often imposed high tariffs on their goods, leading to an increase in smuggling. British smugglers would load up on Caribbean goods, particularly sugar, and take them to the Thirteen Colonies, where these luxuries were always in high demand. To crack down on such practices, the Spanish coast guard often patrolled the Caribbean Sea, stopping and searching any British vessel suspected of carrying contraband.

On 9 April 1731, a Spanish coast guard ship stopped one such vessel, the Rebecca, which had taken on quantities of sugar in Jamaica and was now bound for London. As the Spanish sailors searched the Rebecca, they detained its crew, including the captain, Robert Jenkins. Jenkins, according to his own disposition and some other accounts, was tied to the ship's mast with a rope around his neck and was hoisted into the air three times. The Spanish captain then sliced Jenkins's left ear with his cutlass, which was then torn off by another Spanish sailor. After threatening to treat King George II of Great Britain (reign 1727 to 1760) in the same manner, the Spaniards then left the Rebecca, returned to their own ship, and sailed off.

The Rebecca continued on to London, where the one-eared Jenkins proceeded to tell his story to all who would listen. The story made some traction and was reported in several newspapers – including the Pennsylvania Gazette, edited by an up-and-coming Benjamin Franklin – but the scandal did not fully break until 1738. That year, Jenkins was granted an audience with the Privy Council and even appeared before King George II himself. According to one – likely apocryphal – version of events, Jenkins presented the king with his severed ear pickled in a jar as proof of his sorrowful mistreatment. Jenkins' tale outraged the British public, seeming to confirm their 'Black Legend' prejudices regarding Spanish cruelty. The Tories gained ground in Parliament, politicizing the incident to paint Walpole's Whig government as weak. In March 1739, Parliament passed a vote formally asking the king to seek redress from Spain, on behalf of both Jenkins and other British merchants who claimed to have been similarly mistreated. After Spain refused Britain's demands for restitution, George II declared war on 15 June 1739, an act that was ratified by Parliament four months later.

Shortly after the declaration of war, on 20 July 1739, British Vice Admiral Edward Vernon set sail for the West Indies with a fleet of Royal Navy warships. He arrived at Antigua in early October and immediately set about disrupting Spanish trade in the region. At the end of the month, he dispatched three ships under Captain Thomas Waterhouse to attack the Spanish port of La Guaira in present-day Venezuela and to burn all the Spanish ships in the harbor. Aware that he could not simply blast his way into the port, Waterhouse decided to use deception to gain entry and ordered his vessels to hoist the Spanish flag. The Spaniards, however, had long been expecting an attack and were not fooled by the ruse. As soon as Waterhouse's three ships came within range of their port guns, the Spanish opened fire. The British ships took heavy damage and were forced to withdraw, limping back to Jamaica for repairs. Despite this setback, Vernon was undeterred. On 20 November, he sailed to Portobelo (in present-day Panama) with six ships of the line and captured it in under 24 hours. The British occupied Portobelo for three weeks, destroying its fortifications and seizing the two 20-gun coast guard ships in its harbor as prizes.

The victory at Portobelo was lauded across the British Empire; the capture of a major Spanish port was seen as a great success. Vernon was promoted to admiral, and the Walpole government was pressured into providing additional resources for the war effort. In the spring of 1740, Vernon looked to keep the momentum going by attacking another of the major Spanish ports, Cartagena de Indias, in present-day Colombia. Cartagena, if captured, would be an even more impressive prize than Portobelo. The city itself was heavily fortified and home to over 10,000 people. Its harbor, considered by some observers to be among the finest in the world, was where the Spanish galleons came to take on great quantities of gold and silver from the mines of Peru. Its capture, therefore, would greatly weaken Spain's hold on the West Indies trade. On 13 March 1740, Vernon arrived outside Cartagena with several ships of the line, 3 bomb vessels, 2 fire ships, and multiple transports carrying infantry. After spending a few days reconnoitering the position of the nearest Spanish fleet, Vernon ordered his bomb ships to begin bombarding the city. The Spanish, who had set up a temporary shore battery, returned fire and were able to prevent transport vessels carrying 400 British soldiers from landing. Vernon, finding the city's defenses stronger than anticipated, soon withdrew.

His plans frustrated by the guns of Cartagena, Vernon sought to regain his mojo with another easy victory. On 22 March, he attacked the fortress of San Lorenzo on the Chagres River in Panama. His bomb ships pounded the fortress into submission, and the British admiral accepted the Spanish commander's surrender two days later. Like they had done at Portobelo, the British spent the next few weeks destroying San Lorenzo's fortifications and seizing guns, boats, and anything else of military value. Emboldened by this success, Vernon returned to Cartagena de Indias on 3 May, only to find that the Spanish had not been idle in his absence. A new viceroy, Sebastián de Eslava y Lazaga, had arrived from Spain along with hundreds of seasoned reinforcements, boosting the port city's garrison to somewhere between 3 to 4,000 men (the defenders included 600 Indigenous archers). Having anticipated Vernon's coming, the Spanish arrayed six of their own ships of the line in the harbor to oppose him. This unexpected readiness gave Vernon pause. Rather than roll the dice on a battle and risk throwing away his earlier gains, he decided to once again withdraw to more thoroughly prepare for an attack. He would spend the next half year building an expedition force, one of the largest that a European power had yet deployed in the Americas.

By the end of the year, Vernon had organized a military expedition worthy of Cartagena de Indias' strong defenses. He had put together a fleet of 124 ships, including 29 ships of the line, 22 frigates, several bomb ships, fire ships, and hospital ships, and over 80 transport vessels. The army component of the expedition consisted of 12,000 men, including two regiments of British regular infantry as well as 6,000 royal marines. This number also included four battalions of colonial troops – 3,600 men in total – who had been raised in the Thirteen Colonies. Under the competent leadership of Governor Alexander Spotswood of Virginia, these colonial soldiers were set to rendezvous with Vernon's fleet in Jamaica before the entire force completed its journey to Cartagena. But no sooner had Vernon laid out his grand plans than dire complications arose. In June 1740, Governor Spotswood died in Annapolis, depriving the colonial battalions of their leader. Six months later, Lord Cathcart, who had been slotted to serve as commander-in-chief of the expedition's land forces, also fell ill and died while crossing the Atlantic from London. To make matters worse, as the expedition gathered in Jamaica, the ships' crews and the soldiers aboard the transports began to suffer from diseases like scurvy, typhus, and dysentery. By January 1741, sickness had already killed 500 men and incapacitated 1,500 more.

After forcing 300 enslaved Africans into service to replace his dead sailors, Vernon raised anchor, and his formidable fleet set sail for Cartagena de Indias. The Spaniards, meanwhile, were readying themselves to meet this threat. In charge of the city's defense was Admiral Blas de Lezo, a man who was already a veritable legend on the high seas; having lost an arm, a leg, and an eye in previous battles, he was known as Patapalo, or 'Pegleg', and Mediohombre, or 'Half-man' (at least, he was referred to as such in later sources; there is scant evidence he was known by these nicknames in his own lifetime). Aware that he was heavily outnumbered, de Lezo hoped to hold out long enough to wear the British down through attrition, betting that, unused to the tropical diseases, their numbers would quickly dwindle. On 13 March 1741, the British expedition arrived outside Cartagena. With Lord Cathcart dead, there was no central army commander, and Vernon often found himself bickering with the army officers. Still, the British commanders agreed that any attack from the ocean would be impossible, as Cartagena's walls were too strong. Instead, they would have to gain entry through a narrow, deep-water channel called Boca Chica and assault the city's outer defenses from there. This channel, however, was well-defended by two bastions: Fort San Jose on one side and Fort San Luis on the other.

For the next several weeks, Vernon directed all his firepower on Fort San Luis. Eventually, the British made a breach in its walls and landed their infantry and royal marines in preparation for an assault. On 5 April, the British attacked Fort San Luis by both land and sea. But when the British regulars poured in through the breach, they found the Spanish defenders gone; de Lezo had pulled his men back to the inner fortification of Castillo San Felipe de Barajas the previous night. Though the British had seized control of the city's outer fortifications, it had taken them a month to do so – with more men falling sick and dying every day, they were running out of time. In his desperation to conclude the siege, Vernon drew up a plan for a risky frontal assault on Castillo San Felipe. In the early morning hours of 20 April, 2,000 British and colonial soldiers under Colonel John Grant attempted to storm the fort with ladders. They ran right into the waiting muskets of 1,000 Spanish soldiers, who de Lezo had entrenched below the walls of the fort proper. Repeated volleys of the Spanish muskets stopped the British assault in its tracks, a situation made worse when Cartagena's cannons began to open fire. Once the British began to waver, the Spanish leapt from their trenches and drove them back with a spirited bayonet charge.

By the time the battle was over, the British had lost 600 men, including Colonel Grant, who was killed. Vernon saw the writing on the wall and realized he had neither the time nor the men for another attack. On 9 May, he lifted the siege and returned to Jamaica. As many as 18,000 of his men died during the 67 days he spent outside Cartagena's walls, most of them from disease. The Spanish lost less than 2,000. Of the colonial troops who had served under Vernon, barely 300 survived to return to the Thirteen Colonies. One of these was Lawrence Washington, the elder half-brother of George Washington, future first president of the United States. Lawrence had been sufficiently impressed with his commanding admiral to name his property in Virginia 'Mount Vernon' in his honor. Vernon himself had reached the zenith of his military career. After lackluster success in 1742, he was recalled to Britain. The Walpole government, too, could not survive the disaster of the Cartagena expedition, and Walpole resigned as prime minister in 1742. Thus, the Spanish victory at Cartagena marked the most important moment of the war, not only thwarting Britain's expansionist ambitions but also shaking up its government.

As Vernon was grappling with the Spaniards in the West Indies, warfare also broke out in North America, between the British colony of Georgia and Spanish Florida. Shortly after the outbreak of war in 1739, Major General James Oglethorpe, the founder of Georgia, was instructed by King George II to “annoy the subjects of Spain in the best manner” (quoted by APUSH). Heeding this royal decree, Oglethorpe led 200 men into Florida in December, seizing forts Picolata and San Francisco de Pupo, both situated west of St. Augustine. In May 1740, Oglethorpe returned to Florida with 1,200 men, including Georgia militia and Indigenous allies from the Creek, Chickasaw, and Uchee nations. They laid siege to St. Augustine itself, but due to logistical difficulties, they were forced to lift the siege in July. Oglethorpe returned to Georgia, where he built a fort on the Frederica River in preparation for the inevitable Spanish counterattack.

Such an attack would manifest in the spring of 1742 when Manuel de Montiano, governor of Florida, led 4,000 men into Georgia. On 18 July 1742, the Spanish were advancing along the road to Fort Frederica when they encountered a contingent of Georgia rangers and Native American warriors. Taken by surprise, the Spanish were soon driven back. Oglethorpe took advantage of this small victory by leading the rest of his men out of the fort in pursuit of the retreating Spanish. That same day, he caught up with them, and the two forces clashed at the Battle of Bloody Marsh. Familiar with the terrain, Oglethorpe's Georgia militia and Native American warriors took cover in the dense vegetation, giving them clear shots at the Spanish troops who remained out in the open. When his men started running low on ammunition, Montiano ordered a retreat and ultimately withdrew back into Florida. In March 1743, Oglethorpe led yet another raid into Florida with the goal of capturing St. Augustine. However, he once again met with failure and retreated back into Georgia. This marked the end of the fighting along the Georgia-Florida border for the remainder of the war.

By and large, Vernon's failed assault on Cartagena de Indias marked the end of the war. Shortly after that, the War of Jenkins' Ear – as the conflict would come to be called – would be overshadowed by other wars breaking out all over the world. In Europe, Britain had been drawn into the War of the Austrian Succession in 1740, and in 1744, it would face off with France in North America in King George's War. Though Britain and Spain remained at war, the subsequent battles were more associated with these other conflicts, except for minor privateer actions in the West Indies. It was not until 1748 that the Treaty of Aix-la-Chapelle ended all these wars. The treaty stipulated that the situation in the West Indies return to the way it had been before the war, and that British smuggling in the region cease. Thus, the War of Jenkins' Ear was effectively a Spanish victory.