The significance of the battle of the Argonne forest is that it was the final major offensive of WWI by the allies that caused Germany to surrender.
The war was fought for 47 days from September 26 1918 to November 11 1918. It involved 1.2 million US soldiers and was known as the hundred days offensive.
Knowing that the German could not be everywhere at once, the American army assigned in the Argonne forest managed to achieve in two months what the Allies in over four years of Brutal trench warfare had not managed, by breaking open the German lines and attacking them till they surrendered.