Given the task definition and input, reply with output. This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.

On the French side, planning after the disaster at Wissembourg had become essential. General Le Buf, flushed with anger, was intent upon going on the offensive over the Saar and countering their loss. However, planning for the next encounter was more based upon the reality of unfolding events rather than emotion or pride, as Intendant General Wolff told him and his staff that supply beyond the Saar would be impossible. Therefore, the armies of France would take up a defensive position that would protect against every possible attack point, but also left the armies unable to support each other.
Which disaster made French planning supremely essential?