Declared by the 81st Padishah Emperor Shaddam Corrino IV after news from Count Fenring that Project Amal on Xuttuh was almost complete, the purpose of the Great Spice War was to prevent any Landsraad Great Houses from resisting the use of Amal as a Spice Melange alternative once it was complete. Half the captured spice was to go to the Spacing Guild and the other half would go to CHOAM as a reward for their cooperation. The war eventually ended in disaster for the Imperial House as Amal was never completed to perfection.
In a masterstroke of political maneuvering, Shaddam declared Zanovar his first target, so that while the melange stockpiles there were destroyed, he could also have Tyros Reffa killed. Sardaukar forces descended on an amusement palace and removed spice hidden in the Sandworm exhibit, which had been there for many years. The aftermath left the planet's main cities devoid of life, but failed to kill Reffa. House Tagliari did not respond to the destruction.
The research moon of Richese was targeted after the Emperor was tipped off by an anonymous letter left by House Harkonnen. The Baron Harkonnen had recently been blackmailed by House Richese and so the Baron desired vengeance. The moon had housed a top secret invisibility project at the time the Sardaukar fleet arrived. After the Sardaukar removed the spice hoard the moon was destroyed with atomics, taking with it a fortune in Richesian mirrors worth their weight in spice. Over the next few days a quarter of Richese went blind only to be provided with artificial eyes by the Bene Tleilax. Other humanitarian assistance came from Duke Leto Atreides I at the behest of his mother, Helena Atreides, who is a daughter of Count Ilban Richese.
Although the people of this planet did not posses a hoard at the time of the Great Spice War, they had in the past. Tracked by the Guild and thought to be a source of tainted melange, the planetary government managed to rush a defence force out, but no force could hold back the Sardaukar. Instead, the Sardaukar imposed a blockade after the Beakkali government hijacked two ships full of supplies that "just happened" to also have disease that would kill all vegetation on the planet. The planet then underwent civil war until an Atreides force arrived with supplies.
The final target was meant to remove the last obstacle to Amal dependency. The Spacing Guild thought that the Baron Harkonnen was skimming spice for his hoard and cutting the remainder with a non active ingredient, essentially "watering down" the spice. A massive Sardaukar fleet contained in five heighliners, led personally by the emperor, arrived and locked down the planet. The Guild transmitted codes which disabled all communications and vehicles on the planet. The emperor then ordered the eradication of all life on the planet. At first the Guild thought he was bluffing but then realized that he was not. They immediately withdrew all heighliner use to the Emperor and the five heighliners vanished back into space leaving the Emperor and his men stranded.
The Harkonnens did indeed maintain a spice hoard. However, it was kept on Giedi Prime. An Atreides military force led by Thufir Hawat landed on Giedi Prime and destroyed the stockpile in 10191 AG, during the time the Duke Leto was consolidating his rule on Arrakis.