On 31 December 1543, Henry and Charles had signed a treaty pledging to invade France in person by 20 June 1544; each was to provide an army of no less than 35,000 infantry and 7,000 cavalry for the venture.
Against this Francis could muster about 70,000 men in his various armies.
 The campaign could not begin, however, until Henry and Charles had resolved their personal conflicts with Scotland and the German princes, respectively.
 On 15 May, Henry was informed by Edward Seymour, Earl of Hertford, that, after his raids, Scotland was no longer in a position to threaten him; he then began to make preparations for a personal campaign in France—against the advice of his council and the Emperor, who believed that his presence would be a hindrance.
 Charles had meanwhile reached an understanding with the princes at the Diet of Speyer, and the Electors of Saxony and Brandenburg had agreed to join his invasion of France.

By May 1544, two Imperial armies were poised to invade France: one, under Ferrante Gonzaga, Viceroy of Sicily, north of Luxemburg; the other, under Charles himself, in the Palatinate.
 Charles had gathered a combined force of more than 42,000 for the invasion, and had arranged for another 4,000 men to join the English army.
On 25 May, Gonzaga captured Luxembourg and moved towards Commercy and Ligny, issuing a proclamation that the Emperor had come to overthrow "a tyrant allied to the Turks".
 On 8 July, Gonzaga besieged Saint-Dizier; Charles and the second Imperial army soon joined him.

Henry, meanwhile, had sent an army of some 40,000 men to Calais under the joint command of Thomas Howard, Duke of Norfolk, and Charles Brandon, Duke of Suffolk.
 While Henry continued to squabble with the Emperor over the goals of the campaign and his own presence in France, this massive army moved slowly and aimlessly into French territory.
 Finally, Henry decided that the army was to be split.
 Norfolk, ordered to besiege Ardres or Montreuil, advanced towards the latter; but he proved unable to mount an effective siege, complaining of inadequate supplies and poor organization.
 Suffolk was ordered to attack Boulogne; on 14 July, Henry crossed to Calais and moved to join him.
 A siege of Boulogne began on 19 July—despite the protests of the Emperor, who insisted that Henry should advance towards Paris.

Charles himself, on the other hand, was still delayed at Saint-Dizier; the city, fortified by Girolamo Marini and defended by Louis IV de Bueil, Count of Sancerre, continued to hold out against the massive Imperial army.
 On 24 July, Charles captured Vitry-le-François, from which French forces had harassed his supply lines; finally, on 8 August, the defenders of Saint-Dizier, running low on supplies, sought terms.
 On 17 August, the French capitulated, and were permitted by the Emperor to leave the city with banners flying; their resistance for 41 days had broken the Imperial offensive.
 Some of Charles's advisers suggested withdrawing, but he was unwilling to lose face and continued to move towards Châlons, although the Imperial army was prevented from advancing across the Marne by a French force waiting at Jâlons.
 The Imperial troops marched rapidly through Champagne, capturing Épernay, Châtillon-sur-Marne, Château-Thierry, and Soissons.

The French made no attempts to intercept Charles.
 Troops under Jacques de Montgomery, Sieur de Lorges, sacked Lagny-sur-Marne, whose citizens had allegedly rebelled; but no attempt was made to engage the advancing Imperial army.
 Paris was gripped by panic, although Francis insisted that the population had nothing to fear.
 Charles finally halted his advance and turned back on 11 September.
 Henry, meanwhile, was personally directing the besiegers at Boulogne; the town fell in early September, and a breach was made into the castle on 11 September.
 The defenders finally surrendered a few days later.
On 31 December 1543, Henry and Charles had signed a treaty pledging to invade France in person by 20 June 1544; each was to provide an army of no less than 35,000 infantry and 7,000 cavalry for the venture. Against this Francis could muster about 70,000 men in his various armies.  The campaign could not begin, however, until Henry and Charles had resolved their personal conflicts with Scotland and the German princes, respectively.  On 15 May, Henry was informed by Edward Seymour, Earl of Hertford, that, after his raids, Scotland was no longer in a position to threaten him; he then began to make preparations for a personal campaign in France—against the advice of his council and the Emperor, who believed that his presence would be a hindrance.  Charles had meanwhile reached an understanding with the princes at the Diet of Speyer, and the Electors of Saxony and Brandenburg had agreed to join his invasion of France.
By May 1544, two Imperial armies were poised to invade France: one, under Ferrante Gonzaga, Viceroy of Sicily, north of Luxemburg; the other, under Charles himself, in the Palatinate.  Charles had gathered a combined force of more than 42,000 for the invasion, and had arranged for another 4,000 men to join the English army. On 25 May, Gonzaga captured Luxembourg and moved towards Commercy and Ligny, issuing a proclamation that the Emperor had come to overthrow "a tyrant allied to the Turks".  On 8 July, Gonzaga besieged Saint-Dizier; Charles and the second Imperial army soon joined him.
Henry, meanwhile, had sent an army of some 40,000 men to Calais under the joint command of Thomas Howard, Duke of Norfolk, and Charles Brandon, Duke of Suffolk.  While Henry continued to squabble with the Emperor over the goals of the campaign and his own presence in France, this massive army moved slowly and aimlessly into French territory.  Finally, Henry decided that the army was to be split.  Norfolk, ordered to besiege Ardres or Montreuil, advanced towards the latter; but he proved unable to mount an effective siege, complaining of inadequate supplies and poor organization.  Suffolk was ordered to attack Boulogne; on 14 July, Henry crossed to Calais and moved to join him.  A siege of Boulogne began on 19 July—despite the protests of the Emperor, who insisted that Henry should advance towards Paris.
Charles himself, on the other hand, was still delayed at Saint-Dizier; the city, fortified by Girolamo Marini and defended by Louis IV de Bueil, Count of Sancerre, continued to hold out against the massive Imperial army.  On 24 July, Charles captured Vitry-le-François, from which French forces had harassed his supply lines; finally, on 8 August, the defenders of Saint-Dizier, running low on supplies, sought terms.  On 17 August, the French capitulated, and were permitted by the Emperor to leave the city with banners flying; their resistance for 41 days had broken the Imperial offensive.  Some of Charles's advisers suggested withdrawing, but he was unwilling to lose face and continued to move towards Châlons, although the Imperial army was prevented from advancing across the Marne by a French force waiting at Jâlons.  The Imperial troops marched rapidly through Champagne, capturing Épernay, Châtillon-sur-Marne, Château-Thierry, and Soissons.
The French made no attempts to intercept Charles.  Troops under Jacques de Montgomery, Sieur de Lorges, sacked Lagny-sur-Marne, whose citizens had allegedly rebelled; but no attempt was made to engage the advancing Imperial army.  Paris was gripped by panic, although Francis insisted that the population had nothing to fear.  Charles finally halted his advance and turned back on 11 September.  Henry, meanwhile, was personally directing the besiegers at Boulogne; the town fell in early September, and a breach was made into the castle on 11 September.  The defenders finally surrendered a few days later.
Italian War of 1542–1546