Another defensive alliance formed in September 1672 between Denmark, Emperor Leopold I, the Electorate of Brandenburg, and the duchies of Brunswick-Celle, Brunswick-Wolfenbüttel and Hesse-Cassel. This alliance maintained an army of 21,000 foot and 10,500 horse, and since May 1673, an additional 12,000 men and twenty vessels maintained with Dutch subsidies. At that time in history, Brandenburg was the second most powerful German state , and maintained its own standing army of 23,000 men. The Netherlands had been attacked by the French army in 1672, known as the rampjaar, and the ensuing Franco-Dutch War would only be concluded by the Treaties of Nijmegen in 1678. Roi soleil Louis XIV intended to weaken the anti-French alliance by engaging them on their eastern frontiers: he supported John Sobieski, candidate for the Polish throne, he also supported a contemporary revolt of nobles in Hungary, and aimed at binding the Brandenburgian army in a war with Sweden.
Question: How many duchies joined the defensive alliance with Denmark?
Answer: 3