The first quote looks at Alexander countering the revolt in Thebes:
For a short time the Thebans posted at the Ampheion held their ground, but when they were pressed hard on all sides by the Macedonians and by Alexander, who seemed to pop up everywhere, the Theban horsemen dashed through the city and rushed out into the plain, while the foot soldiers tried to save themselves as best they could. After that, it was not the Macedonians so much as the Phocians, the Plataeans, and other Boeotians who, in a rage, slaughtered the Thebans helter-skelter even when they made no move to defend themselves, falling upon some in their houses, upon others who forcibly resisted, and even upon those who tried to approach the temples as suppliants, sparing neither women nor children.
Any valid history of Alexander has to deal with the body count left in his wake, even in cases like this where his Macedonian troops are not the ones committing the atrocities. Alexander had control over what happened in the city as the next example will make clear, even when blood feuds were being settled. His decision to allow the slaughter of the Thebans must have been meant to send a message to any other “Greek” cities that he would not allow revolt, whether he was nearby or in India. To punish Thebes he stopped his invasion of Asia, setting those plans back several months in order to drive home that point. I’m sure any other city, even if they heard rumors of Alexander’s death (like Thebes had received), would think twice after learning of Thebes’ punishment. How bad was the slaughter? The summary for the section after the above quote describes how it was seen a few centuries later by the author: “Arrian pauses to compare the suffering of Thebes with other great disasters inflicted by one Greek city on another. He finds that all previous cataclysms pale in comparison to the fate of Thebes.”
Alexander could be merciful at times when it benefited him. After his troops take Ephesus, his behavior stands in marked contrast after the recent sack of Thebes:
Reaching Ephesus on the fourth day, Alexander restored all the exiles who on his account had been banished from the city; dissolving the oligarchy, he established a democracy in its place. He then ordered that all the tribute that had formerly been paid to the barbarians [Persians] now be paid to Artemis. When the common people’s fear of the oligarchs had been dispelled, they became eager to kill those who were in favor of calling in Memnon, as well as those who had despoiled the temple of Artemis and those who had thrown down the statue of Philip in the temple and dug up the tomb of Heropythos, the city’s liberator, in the marketplace. Syrphax, his son Pelagon, and the sons of Syrphax’s brothers were led away from the shrine and stoned to death. But Alexander prevented the Ephesians from seeking out and taking vengeance on others, as he realized that if he granted them permission they would unjustly kill the innocent along with the guilty, either to settle private scores or to seize the property of the victims. Never was Alexander’s conduct held in higher esteem than on that occasion, because of what he did in Ephesus.
That last sentence has an echo later on in Book I when Alexander allows his recently-married soldiers to go home for the winter (instead of staying in Asia).
Some of the Macedonians serving with Alexander had married shortly before the expedition, and he recognized that he should not neglect them. Accordingly, he sent them home form Caria to spend the winter with their wives in Macedonia, having placed them under the command of Ptolemy, son of Selukos, one of the royal bodyguards, and two of the generals—Koinos son of Polemokrates and Meleagros son of Neoptolemos—as these men, too, had recently married. He directed them to enlist as many horsemen and infantrymen from the country as they could before returning and bringing back their cohort. And for this deed, more than for any other, Alexander was held in esteem by the Macedonians. He also sent Kleandros son of Polemokrates to levy troops in the Peloponnese.
Alexander’s rashness will emerge over his decade-plus adventure in Asia but at the beginning of his reign and campaign we see a shrewdness calculated for maximum effect and calibrated for the situation.