There are many aspects of Alexander that could be discussed from Book One such as the ingenuity demonstrated in avoiding the Thracian carts or in crossing the Danube with hay-filled tents. There is a lot to look at in his mature military tactics demonstrated at the Granicus River or his ability to improvise during the siege of Halicarnassus. Not that those aspects aren't important, but I thought it worthwhile to observe Alexander’s demonstrations of loyalty and the loyalty he expected to receive in Book One to provide a baseline for comparison during the rest of his campaigns. All quotes are from The Landmark Arrian: The Campaigns of Alexander, translation by Pamela Mensch.
After his father’s death, Alexander insures the Greek cities were still supportive of the League of Corinth with Alexander at its head (Sparta excepted). Hearing rumors of revolt in Thrace, Alexander moves to quell dissension in those dependent territories before beginning his march toward Persia. Alexander makes it clear that he considered having a unified home base a high priority when he returns to Thebes after its revolt. Thebes’ destruction and the death and enslavement of its citizens must have been intended to send a message to any other Greek city contemplating revolt. It certainly worked for Athens, who sent embassies to Alexander to assure him of their support.
Early in his campaign, Alexander’s wrath fell on many Greeks that faced him on the battlefield or tried to subvert him. After defeating the Persian forces at the Granicus River Alexander had the Greek mercenaries fighting for the Persians slaughtered. Mercenaries that survived were sold into slavery in Macedonia. Even with entreaties from Athenian emissaries, Alexander refused to release these slaves. Although Arrian does not explain why, Alexander must have felt the slaves provided insurance for continued Athenian support during his campaigns. (Alexander may have had in mind the Spartan hostages taken in the Battle of Sphacteria during the Peloponnesian War, providing Athens with assurance that Sparta would stop invading Attica.) Alexander equated fighting by Greek soldiers in foreign armies against him as breaking the terms of the League of Corinth—while not technically Greek, Arrian makes it clear Alexander thought he was, whether directly or as leader of the League’s forces.
After Alexander’s victory at the Granicus River, many of the Greek cities in Asia Minor opened their gates to Alexander and were usually rewarded...or at least not punished. Alexander must have realized the implications of his slaughter of Greek mercenaries after the Granicus River battle because he saw determined Greek soldiers at Miletus who appeared ready to fight to the death. Seeing their “nobility and steadfastness”, Alexander offered the Greek mercenaries at Miletus clemency if they fought for him.
Arrian mentions several actions by Alexander calculated to insure or increase his troops’ loyalty to him. Macedonian soldiers that fell at the Granicus River were provided heroic funerals and he provided for their families in Macedonia. Alexander mingled with soldiers wounded in that battle, allowing them to chat and brag about their exploits. Later in the campaign Alexander earned praise and honor from his troops by allowing the soldiers that had been recently married before leaving home to return to their homes for the winter. Alexander administered the cities he took in Asia Minor in such a way that would have earned loyalty from many of them. Tribute rates remained the same or were reduced while many oligarchies were replaced with democratic governments. If a city reneged on its agreement with Alexander, though, they could expect retribution. Aspendos delayed fulfilling their terms of capitulation to Alexander which brought about the doubling of their required payments.
Cities trying to hold out against Alexander, causing him to spend an extended amount of time and effort in conducting siege operations, seem to earn his greatest wrath in Book One. Halicarnassus provides the main example of Alexander’s vengeance when it eventually fell to him. Alexander had the city razed except for a couple of citadels he deemed easier to continue to blockade. It’s as if Alexander takes it as a personal affront if has to lay siege to a city. Is it the extra effort? Impersonal fighting during the siege? Wasted time? It's impossible to say, but I want to see if this trait continues.
The example of Alexander son of Aeropus provides an instructive example of Alexander’s early display of loyalty and those that betray it. This “other Alexander” was brother of the two men who killed his father Philip (as Arrian attributes the plot—that the conspiracy of Philip’s murder had other options or had other possibile murderers is not addressed by Arrian). Since the "other Alexander" immediately supported Alexander’s ascension to the throne he was allowed into the royal inner circle and became captain of the Thessalian cavalry. But... Alexander son of Aeropus was soon rumored to be part of a conspiracy with the Persians to murder Alexander. Instead of acting rashly, Alexander convenes a council with close friends who provide frank assessments, leading to the other Alexander’s arrest. (His ultimate fate is not described here.) As I said earlier, this provides a baseline for any future plots, real or perceived, and how Alexander will handle them.