Henry VIII ascended the English throne in 1509 and within two years began making war against France. The continental gains made by previous kings had gradually slipped away until England controlled nothing more than the port city of Calais. Henry made war against France irregularly over the course of his reign, usually because the French gave support to Scottish independence movements. In 1513 Henry crushed the French at the battle of the Spurs outside Thérouanne just as his subordinate, the earl of Surrey, similarly routed a major Scottish army in northern England at Flodden Field. That double victory allowed Henry to spend some time dealing with domestic matters, but in 1522 he was back in France. Little was accomplished other than ravaging the countryside, and in 1523 a sick and demoralized army returned to England.

Henry spent the next two decades focused on his personal and religious problems, trying to find a wife with whom he could produce a male heir. That pursuit led to his break with the pope and, by extension, Spain, whose King Charles V was the champion of the Catholic Church. Henry's rejection of papal authority further alienated the Catholic Scots, so another Franco-Scottish cabal was in the offing. Only France's King Francis I and Charles V's inability to cooperate for any length of time kept them from allying against England. Henry awaited an invasion, but when none came he prepared to strike first before the continental allies could invade his country. He sent the duke of Norfolk to crush a Scottish uprising in 1543 then, with his rear secure, aimed to cross the Channel.

Charles V was in a sticky political position. Not only was he king of Spain, he was also Holy Roman Emperor, controlling much of central Europe. While he and Francis were both Catholics, they had plenty of conflicts over mutual frontiers. To threaten Charles, Francis entered into an alliance with the Ottoman Turks, always interested in expanding their influence in southeastern Europe. So for Charles, an alliance with Henry (who had rejected the authority of the pope) against a fellow Catholic was balanced by the desire to expand his own holdings against a French king allied with Muslims. Temporarily, Charles ignored his religious position and allied with Henry against King Francis. Both monarchs pledged to send 40,000 men to France in 1544 in a cooperative pincer movement against Paris. However, Henry apparently decided instead to expend his effort securing the region around Calais.

In June 1542, 42,000 English troops debarked at Calais, supported by 4,000 auxiliaries sent from Charles and a number of mercenaries. The force divided, one section under the duke of Norfolk advancing against Montreuil on the Canche River due south of Calais, the other section under the duke of Suffolk marching on the port city of Boulogne. Norfolk's army pursued their siege only half-heartedly, while Suffolk's troops began a close investment of Boulougne on 19 July. Charles protested that Henry was dawdling when he should be advancing on Paris, but Henry replied that the two towns were vital if he was to maintain his lines of supply. The siege of Boulogne became more intense when Henry arrived to take command of the 16,000-man force on the 26th. The lower town was only lightly fortified, and Henry's troops captured it after a heavy bombardment. A Roman-era lighthouse, known as the "Old Man," also fell in the initial attack. The bombardment continued through August. On 1 September Henry launched an assault against the main fortifications protecting the upper town. It was captured, but his men were unable to approach the city's castle. The French resistance and firepower were sufficiently intense to keep the English troops at bay for a time. For another two weeks, Henry's artillerists and engineers did their work, and mines under the castle walls created sufficient damage for the defenders to lose their resolve. On 13 September, they asked for terms. King Henry accepted the surrender of the 1,630 surviving defenders when he entered the town in triumph on the 18th.

Meanwhile, the siege at Montreuil was making no progress. Rather than going there and taking command, Henry stayed in Boulogne, making plans to go home. While doing so, he learned that Charles and Francis had signed a peace treaty on 18 September, just as he was occupying Boulogne. In spite of this news, Henry returned home anyway, leaving Norfolk and Suffolk in France. Norfolk soon abandoned Montreuil, however, learning of the approach of a 30,000-man French army. He fled to Boulogne, then he and Suffolk fled again for Calais, leaving only 4,000 men to defend Boulogne. Francis and his army arrived before Henry's newly won city on 7 October to see that the breaches the English artillery had created in the city walls had yet to be repaired.

On the night of 9 October, Francis decided to launch a night attack. He directed the twenty-three companies of French and Italian infantry to wear white shirts over their armor for greater visibility in the dark, giving this operation the nickname the "camisade of Boulogne." From some inexplicable reason the English were not paying attention to their defenses and the French easily broke into the city. Unfortunately, their operation began falling apart almost immediately. The assault commander was wounded and withdrew, just as rumors began to spread that the English had recaptured the breaches. Rather than retreat in an orderly fashion, the attackers instead abandoned all thoughts of fighting in favor of plunder. Sir Thomas Poynings, commanding the English forces in the citadel, rallied them and launched a counterattack that not only expelled the French forces, but also resulted in the loss of 800 French and Italian dead and prisoners. Francis abandoned the siege with the approach of winter, planning to return the following year.

Without continental allies, Henry expected Francis to launch an invasion of England at the opening of the campaign season of 1545. He stationed three armies along the coast in preparation, but Francis launched little more than small-scale raids. Still, it was enough of a distraction to encourage the Scots to once again rise up and give Henry fits. At Boulogne, the French dug siege lines but did not commit sufficient men to the operation, while the 4,000 defenders were too few to drive the French away. Henry appointed two successive commanders to Boulogne, but neither proved successful in beating Francis' troops. Henry kept Boulogne, but it served him no useful purpose.

Finally, on 7 June 1546, Henry and Francis signed a peace treaty. Henry had assembled yet another invasion force, but in late spring changed his mind. "Perhaps the burden of war had crippled him; perhaps the desperate shortage of food which bad harvests brought in their train and his failure to raise victuals and enough munitions on the continent drove him to peace; perhaps Charles's evident intention to strike in Germany and thus ignore his erstwhile ally pulled him up; perhaps it was all of these things which now made imperative the discretion which the [Privy] Council had urged upon him with great vigour months before and had probably continued to urge thereafter" (Scarisbrick, Henry VIII, pp. 462-463). Still threatening an invasion, however, Henry was able to maintain possession of Boulogne for eight years, at which time it would be returned for a huge indemnity (which Henry was positive would never be paid).

Another section of the treaty said that Henry would not go to war against the Scots unless they violated the peace. He had hoped to get the French to promise a withdrawal of all present and future aid for the Scots, but he was unable to accomplish that. In Great Britain, Henry's last overseas adventure had the effect of keeping Scottish resistance alive. Instead of focusing on Scotland and imposing his will there, Henry could count little gain in the north or in France when the fighting ended.

Henry did get Francis to sign the peace treaty giving him recognition as head of the Church of England and Ireland, so at least one domestic issue was positively addressed. It proved to be a temporary victory, however, for at Henry's death in 1547 his daughter Mary invited papal authority once again to the British Isles.