What are the best PODs for France to get Belgium w/o her neighbors nagging her to relinquish it, or where France beats her enemies severely that they can't anymore challenge French ownership of Belgium?
Easy, Louis XV don't returns it.
But then Britain recruit allies and goes to war with France because balance of power?
It already happened anyways (7 years war).
Probably.It's not that Britain and friends can invade Belgium and take the place back.Exactly.
Can France still fight on at that point, if ever Louis XV rejected the treaty provisions?
Have Elisabeth de Valois give birth to 2 sons circa 1560/1565 (instead of or with her OTL daughters). The eldest becomes King of Spain and the younger is made Duke of Burgundy in 1585. With the death of the Valois rule in 1589, the younger son (let's call him Charles) is put on the throne. Taadaa!
No. Definitely no. There already had been for 250 years a central rule in France : the so-called Salic Law. Never ever would someone on the female line become king. The french ruling classes would rather have a bastard on the male line than someone on a female line.
Not, there are so many PODs.
King Charles III of Francia occidentalis succeeds in retaining the kingdom of Lotharingia and overcomes the betrayal of his main nobles.
Not yet king Charles V's first wife Joan of Bourbon dies premarurely and Charles marries himself Margaret of Male, instead of marrying her with his younger brother Philip the bold d'une of Burgundy.
Louis duke of Orleans, not yet king Louis XII, marries Mary of Burgundy.
Mazarin decides to push war against Spain a bit further in 1659 and to annex then all the spanish Netherlands.
Louis XIV does not screw his campaign in the war of Hollande in 1672. Either he gores for Amsterdam without losing time and takes the city, or he accepts the Dutch proposal of annexing all Dutch territories on the left bank of the Rhine. Annexing the spanish Netherlands a bit later will be a mere formality.
Louis XIV does not push his grandson Philip for the whole spanish inheritance but promotes instead a break-up plan where France gets the spanish Netherlands. This will of course imply war against Britain and the United Provinces.
Louis XV does not make the mistake of handing back the austrian Netherlands which his army had conquered and whose annexion by France Britain was then resigned to accept.
Napoleon does not screw up his russian campaign of 1812 or, although screwing it up, wins a decisive victory in the campaign of Germany of 1813 and strike sa general peace deal in which France retains the Rhine frontier.