Page "Third Anglo-Dutch War" Paragraph 2

Charles had hoped that an attack on the Republic could have begun in 1671, but it had to be delayed for a year because the French needed first to establish secure diplomatic relations with two key German principilaties: the Bishopric of Münster and the Archbishopric of Cologne.

Normally the Spanish Netherlands would act as a buffer between the Republic and France ; to conquer the strongly fortified towns of Flanders and the south of the Republic would both be too slow and too costly for a swift and decisive campaign.

Furthermore, the Holy Roman Emperor Leopold I had promised not to interfere with the French plans, on condition that the Spanish Netherlands would not be attacked.

Therefore it had been decided to let the French army advance through the Bishopric of Liège, a dependency of Cologne that intersected the Spanish Netherlands, and then attack the Republic unexpectedly from the east in its unprotected " soft side ".

Ultimately Münster and Cologne even decided to join the invasion with their armies.