when the prussians, not for military reasons, but out of the mere spite of revenge, burnt down, by the help of petroleum, towns like chateaudun and innumerable villages, was that incendiarism?

Make this proper case.
When the Prussians, not for military reasons, but out of the mere spite of revenge, burnt down, by the help of petroleum, towns like Chateaudun and innumerable villages, was that incendiarism?