You hear a lot after World War II about how the stab-in-the-back myth and how the Peace of Versailles was unnecessarily punitive. But let's put the shoe on the other foot-- what was Germany planning to do to the Allies in the event that the Spring Offensive succeeded in reaching Paris?
^ these answers I've given previously should be pertinent. Although they fluctuated throughout the War, German War Aims generally revolved around the outline of the September Programme of September 9th, 1914:
The general aim of the war is security for the German Reich in west and east for all imaginable time. For this purpose France must be so weakened as to make her revival as a great power impossible for all time. Russia must be thrust back as far as possible from Germany's eastern frontier and her domination over the non-Russian vassal peoples broken.
1.France. The military to decide whether we should demand cession of Belfort and western slopes of the Vosges, razing of fortresses and cession of coastal strip from Dunkirk to Boulogne. The ore-field of Briey, which is necessary for the supply of ore for our industry, to be ceded in any case. Further, a war indemnity, to be paid in instalments; it must be high enough to prevent France from spending any considerable sums on armaments in the next 15-20 years.
Furthermore: a commercial treaty which makes France economically dependent on Germany, secures the French market for our exports and makes it possible to exclude British commerce from France. This treaty must secure for us financial and industrial freedom of movement in France in such fashion that German enterprises can no longer receive different treatment from French.
2.Belgium. Liége and Verviers to be attached to Prussia, a frontier strip of the province of Luxemburg to Luxemburg. Question whether Antwerp, with a corridor to Liége, should also be annexed remains open.
At any rate Belgium, even if allowed to continue to exist as a state, must be reduced to a vassal state, must allow us to occupy any militarily important ports, must place her coast at our disposal in military respects, must become economically a German province. Given such a solution, which offers the advantages of annexation without its inescapable domestic political disadvantages, French Flanders with Dunkirk, Calais and Boulogne, where most of the population is Flemish, can without danger be attached to this unaltered Belgium. The competent quarters will have to judge the military value of this position against England.
- Luxemburg. Will become a German federal state and will receive a strip of the present Belgian province of Luxemburg and perhaps the corner of Longwy.
- We must create a central European economic association through common customs treaties, to include France, Belgium, Holland, Denmark, Austria-Hungary, Poland, and perhaps Italy, Sweden and Norway. This association will not have any common constitutional supreme authority and all its members will be normally equal, but in practice will be under German leadership and must stabilise Germany's economic dominance over Mitteleuropa.
- The question of colonial acquisitions, where the first aim is the creation of a continuous Central African colonial empire, will be considered later, as will that of the aims to be realised vis-à-vis Russia.
- A short provisional formula suitable for a possible preliminary peace to be found for a basis for the economic agreements to be concluded with France and Belgium.
- Holland. It will have to be considered by what means and methods Holland can be brought into closer relationship with the German Empire. In view of the Dutch character, this closer relationship must leave them free of any feeling of compulsion, must alter nothing in the Dutch way of life, and must also subject them to no new military obligations. Holland, then, must be left independent in externals, but be made internally dependent on us. Possibly one might consider an offensive and defensive alliance, to cover the colonies; in any case a close customs association, perhaps the cession of Antwerp to Holland in return for the right to keep a German garrison in the fortress of Antwerp and at the mouth of the Scheldt.
As to your scenario:
what was Germany planning to do to the Allies in the event that the Spring Offensive succeeded in reaching Paris?
While German plans in this event would have probably followed the Programme, as did their treaties with Russia and Romania, it is unlikely that the Germans would have been able to gain this by taking Paris in 1918. By the time of the Gneisenau offensive, Michael, Mars and Georgette had already been launched, and had already failed with horrendous losses.
As to the earlier treaties of Brest-Litovsk and Bucharest:
In the East, extensive annexations were planned, and carried out with the Treaty of Brest-Litovsk in 1918. The Bolsheviks were expecting harsh terms, but both sides, Bolsheviks (who wanted peace at any cost) and the German diplomats, were stunned by the Government's demands.
http://alternatehistory.com/discussion/attachment.php?attachmentid=8876&stc=1&d=1134966449
The establishment of a series of satellite states, to be incorporated into Mitteleuropa, that would essentially be vassals of the Kaiserreich, and amounted to 1/4 of the Russian Empire's population, 1/4 of it's industry, 9/10 of it's coal, whatever gold reserves the Bolsheviks possessed, and the Caucasus oilfields (1/4 of Russia's oil). There were also discussions of direct annexation of a part of Russian Poland, dubbed the 'Polish Border Strip', that was to be resettled with German farmers and soldiers, after close to 1 million Poles and Jews had been 'removed' that is.
That was in March, 1918. In May, the Germans and the Central Powers concluded the Treaty of Bucharest with Romania. Romania had to cede all of Dobruja, which included most of Romania's best ports, to Bulgaria, while the passes in the Carpathians along the border with Hungary and Bukovina were ceded to the Austro-Hungarians, denuding Romania of it's defenses. Romania would also have to fork over it's gold reserves, supply food and coal to the central powers (which Romania could barely do for itself), and lease all of it's oilfields, a major part of the economy, to Germany for 90 years. In return, they got Bessarabia, a Russia province that wasn't even majority Romanian, but at least they got that going for them!
The German Navy had much more concrete war aims, and these involved British, French and Portuguese ports in Africa, the Atlantic and the Caribbean, which would allow the German Navy to challenge Britain and America for world power. They also had designs on the Russian Black Sea Fleet, planning to split it with the Turks and to control ports in, if not the whole of, the Crimea. These plans came to naught with the Russian Civil War and the mutiny of the Black Sea Fleet.
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