OTL, the new German Empire claimed Alsace and two or three-fifths of Lorraine from France as a prize of victory which was justified in Germany from a strategic, linguistic and historic point of view.
One thing that is interesting however, as discussed in this prior thread (Alsace-Moselle), was that although the historic German identity of Alsace-Lorraine was claimed, the new border did not resemble any historic border between France and the Holy Roman Empire.
The linguistic rationale for transferring Alsace has been persuasive to some commentators, but generally not so for Lorraine.
But the linguistic and historic claims did not particularly overlap. In Lorraine France acquired Metz fairly early, but Lorraine was an independent duchy actually after most of Alsace was absorbed.
So, ISTM there was nothing particularly inevitable about the Germans imposing the particular border they did in 1871.
First, what if they had seized more:
A) All the historic territory they took in 1871, plus the rest of Lorraine up to the Moselle river. This takes away some French fortress, shortens the border and puts much of it along a river line.
B) All the historic territory from 1871, plus some additional territory to the west, covering the Briey-Longwy-Thionville iron ore region. This provides more natural resources and cuts of Luxembourg from France completely.
C) Alsace, plus all Lorraine, as defined as a modern region of France. This border is about as short as OTLs, but is further forward and provides more resources.
D) Alsace, plus all Lorraine, according to the prerevolutionary borders of the province. This grabs yet more resources, restores some of the HRE western boundary, and makes it easier to deal with France without going into Belgium, although it is very awkwardly shaped.
E) Alsace, Lorraine and Franche-Comte - this weakens France even more and reestablishes a historic western border of the HRE that lasted for centuries. Granted its not a complete restoration because there's no grabbing of Belgium, Artois and French Flanders, but messing with Belgium and the Channel ports is a sure-fire way to bring on war with Britain.
- alternatively, what if they took less than in OTL-
F) Alsace alone
G) Alsace plus some bordering portions of Lorraine but not Metz or anything south or west of that city
Obviously, the larger the annexation the more French-speaking people there are to manage.
At the same time, given a choice between absorbing more or less territory, there's a realpolitik argument for taking more, because France will be revanchist about any annexation at all, no matter how small.
One thing that is interesting however, as discussed in this prior thread (Alsace-Moselle), was that although the historic German identity of Alsace-Lorraine was claimed, the new border did not resemble any historic border between France and the Holy Roman Empire.
The linguistic rationale for transferring Alsace has been persuasive to some commentators, but generally not so for Lorraine.
But the linguistic and historic claims did not particularly overlap. In Lorraine France acquired Metz fairly early, but Lorraine was an independent duchy actually after most of Alsace was absorbed.
So, ISTM there was nothing particularly inevitable about the Germans imposing the particular border they did in 1871.
First, what if they had seized more:
A) All the historic territory they took in 1871, plus the rest of Lorraine up to the Moselle river. This takes away some French fortress, shortens the border and puts much of it along a river line.
B) All the historic territory from 1871, plus some additional territory to the west, covering the Briey-Longwy-Thionville iron ore region. This provides more natural resources and cuts of Luxembourg from France completely.
C) Alsace, plus all Lorraine, as defined as a modern region of France. This border is about as short as OTLs, but is further forward and provides more resources.
D) Alsace, plus all Lorraine, according to the prerevolutionary borders of the province. This grabs yet more resources, restores some of the HRE western boundary, and makes it easier to deal with France without going into Belgium, although it is very awkwardly shaped.
E) Alsace, Lorraine and Franche-Comte - this weakens France even more and reestablishes a historic western border of the HRE that lasted for centuries. Granted its not a complete restoration because there's no grabbing of Belgium, Artois and French Flanders, but messing with Belgium and the Channel ports is a sure-fire way to bring on war with Britain.
- alternatively, what if they took less than in OTL-
F) Alsace alone
G) Alsace plus some bordering portions of Lorraine but not Metz or anything south or west of that city
Obviously, the larger the annexation the more French-speaking people there are to manage.
At the same time, given a choice between absorbing more or less territory, there's a realpolitik argument for taking more, because France will be revanchist about any annexation at all, no matter how small.