Alexander at Troy and Egypt

Alexander visited Troy so for political and personal reasons. When his ship sailed up to the shore, he waded forth in full armor, and threw his spear ashore to claim the land. He respected the men who died in the Trojan War so much he worshiped them, and he greatly respected Homer as well. When he went there, he made a highly symbolic gesture; he replaced his weapons in Athena's temple with he ones used in the Trojan War. By doing this, he claimed, without words, that he was going to be a hero, and now the gods and the soldiers that fought in the Trojan War were on his side. While visiting Troy, he also liberated many cities, gaining him support and admiration.

For Alexander, Egypt didn't need to be conquered.