The frontier opens

On 10 May 1940 German forces invaded the Netherlands, Belgium and Luxembourg. The offensive overturned the neutrality on which those countries had relied and opened the western campaign across a broad front. It was not a single column making a single breakthrough. Aircraft, airborne troops and ground forces struck at different places, forcing defending governments and headquarters to assess several emergencies at the same time.

For civilians, national strategy became an immediate problem of survival. Roads carried military columns and people trying to escape the fighting. Families leaving their homes could not know which town would remain safe, which bridge would still be open or where the next attack would fall. The refugee photographs in this collection belong inside the campaign's story: the battle passed through inhabited countries, not empty space between headquarters.

Bridges, airfields and a Belgian fortress

German airborne operations sought to seize places that could slow the ground advance: bridges, airfields and other key points. Their purpose was practical. A bridge captured intact could carry an army forward; a demolished bridge could force engineers, vehicles and supplies to wait. Airborne troops offered a way to reach such places before a conventional ground attack could get there.

The assault on Belgium's Fort Eben-Emael became the most famous example. German glider troops landed on its upper works and used explosive charges against important positions. The action helped undermine the defenses covering the approaches nearby. It did not prove that every fortification was obsolete or that the whole Belgian Army had ceased fighting. It demonstrated how a carefully prepared attack could exploit a particular defensive weakness.

Elsewhere, airborne attacks produced fighting rather than automatic success. Aircraft on a map can appear to leap over obstacles without cost. The men who landed still had to hold their objectives, link up with ground forces and survive counterattack. The German offensive's speed emerged from the interaction of these operations, not from airborne troops acting independently of the armies following them.

The Allies move into Belgium

The German attack triggered the Allied advance. British and French formations moved toward their planned positions in Belgium, while a French force pushed toward the southern Netherlands under the Breda extension. The advance was an attempt to carry out the coalition's prepared defense, not an aimless march toward an obvious disaster. The central difficulty was that the enemy's northern attack confirmed what Allied headquarters already expected to see.

French and Belgian forces resisted, and British troops moved toward the Dyle position. Fighting in Belgium was substantial. Treating the whole northern offensive as a diversion must not imply that it was a sham: it captured territory, killed soldiers and threatened important objectives. Its additional value to Germany was that it fixed Allied attention and drew major formations away from the place where the southern breakthrough was being prepared.

Commanders now faced the problem at the heart of coalition warfare. Armies with different headquarters, national responsibilities and communications had to act together while the situation changed. A withdrawal by one force could expose another. A decision made for the security of one country might affect an adjacent army's position. Coordination became harder at the very moment when speed mattered most.

Rotterdam and the Dutch defeat

The Netherlands faced attack from the air and across its land frontier. Dutch resistance did not prevent the campaign from turning quickly against it. On 14 May German bombers devastated central Rotterdam. The destruction of a major civilian city, and the threat of further bombing, gave the military emergency an additional human and political weight.

The principal Dutch capitulation followed on 15 May. This date should not be used to erase every subsequent act of Dutch resistance or all fighting outside the main surrender's scope. Nor did defeat end the Netherlands' participation in the wider war. Occupation and exile opened another part of the country's wartime experience. For the Allied armies advancing from France, however, the prospect of establishing the intended northern connection had deteriorated sharply.

The attack taking shape farther south

While the northern battle demanded attention, the main German concentration passed through Luxembourg and the Ardennes. Forests and restricted roads made that movement difficult, but difficulty was not impossibility. The decisive assumption was not simply whether soldiers or tanks could travel through the region. It was how quickly a large, supported force could arrive at the Meuse and force a crossing before the defense was adequately reinforced.

The German plan linked the two fronts. The armies advancing into Belgium were moving toward one expected battle while the southern thrust threatened to pass behind them. A strong force in the wrong place could still win local engagements and lose its connection to the rest of the campaign. That is why the opening days cannot be explained by comparing national totals of tanks or soldiers alone.

Read the map in two directions

To understand these days, follow two movements separately before putting them together. First trace the Allied advance northeast into Belgium and toward the Netherlands. Then trace the German approach west through the Ardennes toward the Meuse. Neither arrow tells the story alone. Their relationship reveals why the threatened crossing at Sedan would become more consequential than the Allies' first responses to the northern invasion.

By 13 May German forces were forcing their way across the Meuse at Sedan. Only three days had passed since the offensive began. The Allies still had armies in the field, men willing to fight and weapons capable of stopping German machines. What they were beginning to lose was the time and geographical freedom needed to bring those strengths together. The next chapter follows the crossing and the drive to the Channel, when a threatened flank became a severed campaign.