If I remember right from the guided tour I took (I was a little distracted by all those giant family portraits and all that 24-karat gold leaf on the ceilings), it was built after the War of Spanish Succession on grounds that the crown offered to the Duke as a recompense for valor in battle. But even though the palace has its origins in war, the main dining room is devoted to peace, with trompe l'oeil paintings of deputies from various countries coming together in a grand colonnade. The rest of the state rooms I saw are very heavily decorated in English and French baroque styles, with sweeping views of the palace grounds.
I spent most of the day wandering around outside, marveling at the expanses of sloping lawns and vistas of the tree-lined lake. The ground were carefully landscaped by one of the previous dukes, and the lake was actually artificially dug out, but they were apparently very good at landscaping back then, because it looks very natural and the prospect from almost every point in the park is very pleasing to the eye. Here are some photos, then, from my rambles that day.