Wasn't the initial German success in Operation Michael the result of terrible mistakes of British commanders and also French commander Duchesne - who did not understand what is "defence in depth" (for example British forces used several lines of trenches, but first line was manned by largest forces, while each subsequent line was defenced by smaller forces - while it should be totally inversely to work properly)? Later in July of 1918 when Germans launched another attack near Reims, French commander Gouraud - who understood how proper defence in depth should look like (first "defensive zone" was weakly manned - and it "absorbed" German artillery preparation fire; further "defensive zones" were stronger - each subsequent line of trenches being defended by stronger forces) - repulsed them quite easily. And I suppose that without American reserves a competent French or British commander would also be enough to stop them.
BTW - was Operation Michael really an attempt to win the war, or just an attempt to improve German situation in peace talks ???
France and to a lesser extent Britain were played out, but the Americans had colossal amounts of manpower
Wasn't Britain played out to a greater extent than France when it comes to manpower reserves / replacements availability?
It was Britain not France (maybe France too, I'm not sure) which reduced size of its divisions from 12 to 9 battalions after 1917.
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BTW - I found the following info regarding casualties in those last German offensives of the war:
Operation Michael (Kaiserschlacht) 21 March - 4 April 1918 - ca. 240,000 Germans (40,000 on 1st day); 180,000 British (40,000 on 1st day); 70,000 French
Allied losses in that Operation Michael included 90,000 prisoners of war - mostly British.
German losses were 240,000 out of 1 million and several hundred thousands who took part - so very heavy losses.
Operation Blucher-Yorck (battle of the Aisne) 27 May - 6 June - ca. 130,000 German casualties; ca. 130,000 Allied casualties
Second battle at the Marne, 15 July - 6 August - ca. 130,000 Allied losses (95,000 of them French); ca. 139,000 German losses
But Allied losses in materiel were much greater than German (BEF lost huge amount of artillery pieces captured by Germans, for example).
In terms of manpower losses, 40,000 German vs 40,000 British was still much better than 57,000 British vs 9,000 German (1st day of the Somme). Also German territorial gains in that offensive were significant (as well as amount of materiel captured). In WW1 conditions (in which usually attacker suffered huge losses without any benefits), it was definitely a success to achieve so much success and territorial gains at similar human cost to that suffered by the enemy.
Had the United States not joined the war in 1917, Britain would have run out of food and of the stuff necessary to feed the gaping maw of its military-industrial complex
But Germany did run out of food and other necessary stuff already in 1917, didn't it ???
Moreover - Germany did manage to eliminate Russia from war, but also a couple of Germany's allies were practically eliminated from war by 1917.
So the overall balance of forces would not change that much. BTW - in Operation Michael also German veterans of the Eastern Front took part.
Operation Michael offensive was spearheaded by veterans, gathered in so called Angriff-divisionen (Assault divsions). But as we can see, Germans suffered huge losses in Operation Michael - which means that after it ended, a lot of their veterans from Angriff-divisionen were dead or wounded.