WHY THE CENTRAL POWERS LOST THE FIRST WORLD WAR

By mid 1918, the Allies were winning battles; the Central Powers were losing them.
The Allies were gaining ground in the Middle East, the Balkans and the Western Front. The Central Powers were retreating on all sides. Even though the German Army was still on French soil and in surprisingly good order, it was only a matter of time before they would be pushed back into Germany.
The Allied generals had learned valuable tactical lessons from the first three years of the war and put them into practice.

The Allied command structure was unified under Marshal Foch in spring 1918.
Tanks, aircraft, artillery and infantry were integrated into coordinated plans with achievable objectives.
The Allies had won the battles of technology, supply and manpower.
The Allies had built over 4000 tanks, the Germans just 20. The Allies had sufficient artillery and manpower on the Western Front to be able to launch a succession of attacks on the German line without having to move and re-group resources each time. The Germans had a manpower shortage: they had guns in France without gun crews to fire them.

The Central Powers were militarily, politically and economically weaker than the larger Allied coalition they faced.
As the Allies grew stronger, Germany's alliances were crumbling. By March 1918, Austria-Hungary was on the verge of bankruptcy and famine - on one occasion, it was even forced to steal a grain barge bound for Germany as it sailed up the Danube. Germany itself was being starved of food and all goods as a result of the British Navy's blockade of her ports in the north. German troops were poorly equipped and most available supplies were sent to the war effort leaving the people of Germany very short of food. Many on both fighting and home fronts had grown tired of the war; they wanted peace, food and democracy. Turkey was asking for an armistice by September 1918. When Ludendorff learned that Bulgaria had also requested an armistice he had a fit. Germany could not fight on alone against the Allies.

The entry of the United States into the war made ultimate Allied victory certain.
America's contribution to the Allies' success was not particularly the result of anything it did on the battlefield, but rather was the threat of its vast potential. The United States was larger than Germany in terms of both population and industrial output. Thus the United States, particularly when combined with the British Empire and France, had the potential to overwhelm the German army. The one constraint was time. The German high command had gambled that their U-boat campaign could knock Britain out of the war. When that campaign failed, it was clear that time was on the side of the allies. In 1917, the United States army was miniscule - smaller than that of Belgium. It would take time to train and equip millions of soldiers. Similarly, it would take time to shuttle them across the Atlantic Ocean. In practice, American forces did not begin to fight in significant numbers until the summer of 1918, and even by the end of the war only one in ten of the Allied front line soldiers was American.

The failure of the Ludendorff offensives.
During the Ludendorff offensives the Germans killed a lot of allied soldiers, but they lost more men than the allies. The failure of the offensives drained the already depleted German resources, and the prospect of endless supplies of American men, money and munitions flooding into Europe completely obliterated all hopes of a German victory.
By autumn 1918 Germany's commanders knew they couldn't hope to win. After years of keeping the politicians in the dark, the military leaders gave them the job of suing for peace.