Detailed Instructions: 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.
Q: John's position in France was considerably strengthened by the victory at Mirebeau, but John's treatment of his new prisoners and of his ally, William de Roches, quickly undermined these gains. De Roches was a powerful Anjou noble, but John largely ignored him, causing considerable offence, whilst the king kept the rebel leaders in such bad conditions that twenty-two of them died. At this time most of the regional nobility were closely linked through kinship, and this behaviour towards their relatives was regarded as unacceptable. William de Roches and other of John's regional allies in Anjou and Brittany deserted him in favour of Philip, and Brittany rose in fresh revolt. John's financial situation was tenuous: once factors such as the comparative military costs of materiel and soldiers were taken into account, Philip enjoyed a considerable, although not overwhelming, advantage of resources over John.[nb 6]
A:
What victory strengthened John's position?