paragraph: Alexander began his reign by eliminating potential rivals to the throne. He had his cousin, the former Amyntas IV, executed. He also had two Macedonian princes from the region of Lyncestis killed, but spared a third, Alexander Lyncestes. Olympias had Cleopatra Eurydice and Europa, her daughter by Philip, burned alive. When Alexander learned about this, he was furious. Alexander also ordered the murder of Attalus, who was in command of the advance guard of the army in Asia Minor and Cleopatra's uncle. Attalus was at that time corresponding with Demosthenes, regarding the possibility of defecting to Athens. Attalus also had severely insulted Alexander, and following Cleopatra's murder, Alexander may have considered him too dangerous to leave alive. Alexander spared Arrhidaeus, who was by all accounts mentally disabled, possibly as a result of poisoning by Olympias. News of Philip's death roused many states into revolt, including Thebes, Athens, Thessaly, and the Thracian tribes north of Macedon. When news of the revolts reached Alexander, he responded quickly. Though advised to use diplomacy, Alexander mustered 3,000 Macedonian cavalry and rode south towards Thessaly. He found the Thessalian army occupying the pass between Mount Olympus and Mount Ossa, and ordered his men to ride over Mount Ossa. When the Thessalians awoke the next day, they found Alexander in their rear and promptly surrendered, adding their cavalry to Alexander's force. He then continued south towards the Peloponnese. Alexander stopped at Thermopylae, where he was recognized as the leader of the Amphictyonic League before heading south to Corinth. Athens sued for peace and Alexander pardoned the rebels. The famous encounter between Alexander and Diogenes the Cynic occurred during Alexander's stay in Corinth. 
question: Why did Alexander order the murder of Attalus?
answer: Severely insulted Alexander