Interestingly enough, it was Italy which actually won the war for the Allies. Most attention is directed at the history of major battles on the Western Front, but even with the influx of American troops and the collapse of moral in Germans in the trenches at at home, the German lines had stabilized and were still in France and Belgium when the High Command demanded the government ask for an armistice. The reason Germany's General Luddendorf lost his nerve and the Germans realized the war was lost involved an offensive by the Italian army against the Austro-Hungarian forces.
The Austrian military had been so beaten down by this time that the Italians finally broke through their lines and rounded up tens of thousands of soldiers. The Austrians simply wouldn't fight any more. This led to Austria's surrender, and this meant that the Allied forces bottled up in Salonika for most of the war now had a clear path through Austria to the underbelly of Germany. The Germans had no troops to oppose them, and no transport or supplies had they possessed any. By the beginning of October, 1918, the German High Command accepted a new Chancellor, Prince Max of Baden, and demanded that he seek an immediate armistice.
I strongly recommend No Man's Land, by John Toland. For a very detailed tactical and strategic analysis, I recommend B.H.L. Hart's study of strategy through history, On Strategy.
Curiously, in both World Wars, Italy has tacitly switched sides! In 1882, a relatively recently unified Italy joined with Germany and Austria-Hungary, thereby creating the Triple Alliance, which lasted until the spring of 1915. In 1911, Italy declared war on the Ottoman Empire during what became to be known as the "Second Balkan Crisis" conquering Tripoli and the Dodecanese Islands, competing in the colonial race in which the other major European powers were engaged. Italy had unified from city-states to a nation in the 1860's; however, there were areas of mixed Italian populations, mostly around its eastern borders, known as Italia irredenta, or "unredeemed Italy," from where the English word "Irredentism" derives. These areas included Trieste, Dalmatians Nice, and Savoy, and Italian Nationalists wanted them incorporated. In 1915, having come into conflict with Austria-Hungary over these border areas, Italy quietly drifted away from the Triple Alliance, and signed a secret treaty (Treaty of London) where, if the Triple Entente (Britain, France and Russia) proved victorious, Italy would gain these areas. Italy also desired to expand colonial operations in Africa at German expense, but at the conclusion of World War I, the former Germanic colonies in Africa and the Near East all went to France and Great Britain.
A History of the Modern World, Palmer & Colton, pg. 680-686, 1978.