In US history especially, the first World War is often treated as a side note of President Wilson's term of office - a major side note, granted, but still not a serious focus of the course (due to the relatively short time we were involved, most likely). I am curious how well the Allied forces were doing before we entered the war. Were the French, English, Russian, and Italian forces winning?
^ this previous answer I've given should be pertinent.
I am curious how well the Allied forces were doing before we entered the war. Were the French, English, Russian, and Italian forces winning?
They certainly weren't losing, and they'd retrieved the strategic initiative after the Central Powers had held it more or less continuously from August 1914 to June 1916. The Germans were faced with a manpower crisis, and had resorted to increasing militarization of their government and the state in general, under Ludendorff and Hindenburg. The Blockade had begun to bite, and American entry would make it virtually air tight.
At the same time, things weren't perfect for the Allies either. America's entry into the war coincided with the German Navy resorting to unrestricted submarine warfare, which inflicted serious losses on Allied shipping. The Russian Empire experienced a revolution in Petrograd which led to the abdication of the Tsar and the establishment of a Republic; the Russian Army was in very rough shape after the Brusilov Offensive in 1916, and there were worries that the sorry state of Russia's war effort might only worsen. In Britain, credit with American banks (specifically J. P. Morgan) was drying up, and Adam Tooze has suggested in his book The Deluge that without direct government-to-government loans that were available due to American entry, the British would not have been hard pressed to carry out the Ypres Offensive that summer (3rd Battle of Ypres/'Passchendaele'). The French were also feeling the affects of their 1914-16 losses more acutely, and the abysmal results of the Nivelle Offensive that spring triggered a mutiny that paralyzed much of the French Army from May to early July 1917.
"Victory inclining to us" is the way British staff officer (and future CIGS) Henry Wilson described it. The threat the Germans posed was enough to justify American entry, and the Allies were in a position that could at least offer the potential for victory, with American support of course.