Deleted member 1487
That is assuming that the colonies would agree. The willingly provided manpower, but fiercly resisted conscription. I don't think that that will provide a source for manpower in the end. Besides, the British could not force the dominion to send men. And the colonies were another story...
Actually not quite, provided US raw materials are still available.
OTL, by the end of the war, Germans had mobilised classes 1918, 1919 and 1920 ( ie 16 year old ), France had mobilised classes 1918 and 1919 and Uk only class 1918.
So manpowerwise, the entente had a little more reserves than Germany.
Considering food production, the crisis that Germany had OTL will not go away and has no equivalent on the entente.
So, yes, it's bad for the entente if US manpower is not known to be available soon ( esp on a morale level, unless an alternative is found, see below ), but the situation is not as bad as it is for Germany.
Finally, there's a ressource the entente didn't fully tap OTL but which they may have to if US is not seen as coming. the colonies. The entente never introced full conscription in the colonies ( commonwealth excluded ). Even a partial conscription would have given enough manpower reserve to equal anything the US did OTL. Of course, there would be a sharp political price to pay after the war. But after the war is after the war.