You're all beating around the bush. Entente's scale of war effort was unsustainable without further American loans for which they ran out of credit. It was only sustained because Congress allow led unsecured loans which only happened because it entered the war on Entente's side. America's critical assistance to the Entente against the Spring Offensive wasn't military it was economic
Every thread imagining a better German performance in 1918 hits some variation of this point. Understandably. It’s the only possible hint of an equalizer between the two alliances. And it’s a reasonable point to push. But to steal a line from one of the many adaptations of Murder on the Orient Express: “it suffers only from the defect of not being factual”. Or at least, not completely so.
For starters, though American production was certainly an important adjunct to that produced by the Entente directly the Entente out produced the CP in basically every category even without American production. So a cut off of American production would not be enough to overcome the deficit that Germany faced against the British and French.
Second, American finance was used to purchase American goods. Mostly (at least by dollar value) manufactured goods. The lack of it would mean a lack of ability to purchase in America, but would not hamper purchases within the British Empire or in other neutrals. Don’t get me wrong, the loss of American materials would be keenly felt. But it would bot be likely to overcome German disadvantage.
Third, the Entente situation was not quite as bad as it is sometimes made out to be. What is usually referenced in this regard is the statement by Chancellor of the Exchequer Reginald McKenna in late 1916 that Britain could not continue purchases for long. This statement needs a bit of nuance. Of the $4 Billion in US denominated securities (useful for securing loans in the US) only $1.5 billion has been gathered by the government to that point. McKenna was an ideological liberal Chancellor under an equally ideologically liberal PM. At this stage in time that meant a commitment to volunteerism and a distaste for conscription of either men or finance. So what McKenna meant was that they could not continue purchase at current rate without resorting to measures that were ideologically unacceptable to the Liberal leaders. A few weeks later Lloyd-George launched his coup and Asquith and McKenna were out. By January new sequestration measures had been launched to gather more securities. In addition, at least one of the several classes of banks existant in the UK at the time had become basically inert due to the circumstances of the war. Yet their gold deposits were also untapped. The Securities alone would have kept Entente imports from the U.S. flowing well into 1918 at minimum. Helped along by the fact that the French had negotiated a large loan prior to Wilson’s attempts to pressure the Entente through the Fed. This would have got them through to late spring 1918 without requiring any further security (which was handled by London anyway).
And finally, Wilson’s instructions to the Fed had a specific purpose. Wilson was determined that the US be the arbiter of the peace settlement and of the new world order that would arise. Through mid and late 1916 the Germans had been more amenable to Wilson’s attempts at mediation. At least partially due to Falkenhayn recognizing that victory was not possible and a political solution was required, which he communicated to his government. With this opening Wilson needed to try and pressure the Entente to also come to the table. Hence the instructions to the Fed (against the wishes of Reserve leadership) to move against Entente lending. However, Falkenhayn’s replacement with the more optimistic Hindenburg and Ludendorff, and the slow progress of the negotiations with the US due to the coming American election caused a breakdown in German-American relations. The diplomatic situation was already deteriorating by late November. The intention of Wilson’s actions was to force a settlement on both sides. It was very much not to aid the German war effort, as the US generally supported the Entente cause and was much more closely tied to it. If Wilson’s actions appeared to be shutting off Entente trade with the US entirely (hurting the American economy) and improving Germany’s chances, it would be an own goal on his part to not soften his stance on Entente lending.
You're putting the cart before the horse. Spring Offensive was only launched to prevent American armies from entering France because they would be too numerous to defeat. Without American entry there won't be a Spring Offensive but a better planned offensive with a much weaker Entente.
Not necessarily . Germany could not outlast or outspend the Entente. They knew that. Their whole strategy was to knock one of the opponents out of the war to focus on the other. By 1918 this had seemed to pay off with Russia. The next obvious objective is to either sue for peace with the remainder or try and enforce one. The parties in place in 1918 seem unlikely to be willing to give up enough to make the first possible. So the only option is to try and enforce a peace using the recently freed up eastern troops. Which would basically be what happened. IOTL the German attack effectively spoiled a planned Entente attack in late spring/early summer. If the Germans wait to launch their own attack they may actually be spoiled in tern.
It’s also probably incorrect to say that the failures of the Spring Offensive were due to the need to rush it before American troops arrived. Some of those can be put on its architect, some on the tendency of the German staff to favour objectives over logistical reality. I think the bulk of the blame, however, has to rest on the general impossibility of the concept. The German Army simply could not move far enough, fast enough, and still be capable enough of combat at the end of it to achieve anything like the decisive result they needed. It’s unlikely even the Entente armies with a much more robust tail, could have done so.