The United States of America under the leadership of President Theodore Roosevelt (who won the 1912 presidential race as nominee of the Progressive Party) declared war on the Central Powers on April 25th, 1916. However, as most of the citizenry favoured isolation, Roosevelt's gamble failed to pay off immediately, and the relatively tiny United States Army could not muster considerable strength in Europe until a year later. Regardless, this state of affairs put Germany in an extremely dire situation, though the practical collapse of the Russian Army later that year allowed the Deutsches Heer, the Austro-Hungarian K.u.K. and the Italian Army to transfer dozens of divisions westward. Fortunately, preparations for Unternehmen Zeidrack were almost complete later that year.
On the 26th of October, 1916, 54 German divisions went on the assault in the region around the city of Dijon, beginning the Battle of Dijon. They were reinforced by numerous newly created Sturmtruppen units, as well as the first mass-produced German tanks, which faced off against the far heavier but less mobile British Mark Is to the surprise of German leadership. Despite a defiant defence, and grievous German losses, all Entente forces in the area were routed, and mobile warfare resumed. German air superiority allowed their ground units to manoeuvre freely. The Deutsches Heer pushed in a wide flanking manoeuvre parallel to the Saone and Loire rivers, threatening the rear of the French Army in the Alps. Temporarily unable to respond to the new weapons and tactics that the Germans had brought about so suddenly, the French decided to retreat hastily towards Guyenne and Gascony, ceding some of France's most important industrial areas and ore mines, as well as the French Alps. Italian troops crossed to reinforce the southern sector and mop up pockets of resistance, freeing Germany's assault units for further actions. Entente commanders were betting everything on a rapid and decisive influx of American troops which would allow them to win the war through attrition.
By February of 1917, though the northern Deutsches Heer units were in no position to attack across the Seine (mainly entrenched and with low concentrations, all bridges destroyed long ago), the southern German-Italian task force threatened to bypass this line entirely through the south. The French government decided to fight until the last man, though morale in the British Expeditionary Force had sunk to an all-time low. The British leadership, desperate to find a victory to report back home, sailed to meet the German fleet off the coast of Jutland.