A pre-war plan laid out by the late Marshal Niel called for a strong French offensive from Thionville towards Trier and into the Prussian Rhineland. This plan was discarded in favour of a defensive plan by Generals Charles Frossard and Bartélemy Lebrun, which called for the Army of the Rhine to remain in a defensive posture near the German border and repel any Prussian offensive. As Austria along with Bavaria, Württemberg and Baden were expected to join in a revenge war against Prussia, I Corps would invade the Bavarian Palatinate and proceed to "free" the South German states in concert with Austro-Hungarian forces. VI Corps would reinforce either army as needed.
From Thionville towards Trier, what was the final destination of the offensive?
the Prussian Rhineland