When he became king, he already owned Macedonia and Greece. When he conquered Persia, he crowned himself king of Persia as well. As any people will do when occupied, the Persians gradually became more and more Macedonian, (a Greek culture) using phalanx-capable soldiers, speaking and writing Greek, using Greek names, ect. In this way, he united the Macedonian and Persian cultures.
Cities under Alexander's rule flourished without fear of attack. This protected and promoted trade which lead to the emergence of primary routes like the Silk Road. Along the silk road Hellenic civilization, language and culture were spread and fused with local culture influencing religion (Buddhism, Judaism, Christianity), art, science and philosophical ideas . These Hellenized cultures too were spread by missionaries and traders (now able to communicate with the Greek lingua franca) and continued for hundreds of years after Alexander's death until new empires emerged and fused Hellenism with their own culture spreading the Greek civilization further still, impacting the whole world to the present day.
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He hoped that he could introduce Greek culture into the ex-Persian Empire which was now his own empire. It affected only the upper class, so the mainstream people continued on in their normal ways. His early death precluded him from taking this further, so we don't know how successful it might have been. The eastern areas soon reverted to their old cultures, or were over-run with invading peoples.
Persian
Alexander the Great aimed to unite his empire by implementing various strategies. He encouraged the assimilation of different cultures by adopting Persian customs and appointing Persians to key positions. He also used intermarriage between his Greek soldiers and Persian women to foster cultural integration. Additionally, Alexander promoted the use of a common language, Greek, as a unifying force among diverse peoples.
It left the Persians with no legitimate king to unite opposition against his ongoing conquest of the Persian empire. He was then dealing with separate kingdoms and tribes.
Threat of annihilation by the Persian invasion
He provided them a share in the spoils of conquest of the Persian Empire using Greek city soldiers, while using his influence in the Amphictyonic League to keep the Greek cities quiet.
Persian
Alexander the Great aimed to unite his empire by implementing various strategies. He encouraged the assimilation of different cultures by adopting Persian customs and appointing Persians to key positions. He also used intermarriage between his Greek soldiers and Persian women to foster cultural integration. Additionally, Alexander promoted the use of a common language, Greek, as a unifying force among diverse peoples.
Alexander sought to create an empire, and by subjugating and organizing the lands more native to him (although as a Macedonian, he was not quite considered "Greek" by the standards of the day) he created a strong foundation to the empire that would span across the known world.
Yes and no because some cultures can not unite
Unite.
It left the Persians with no legitimate king to unite opposition against his ongoing conquest of the Persian empire. He was then dealing with separate kingdoms and tribes.
Threat of annihilation by the Persian invasion
He did
Self defence.
His father had a dream to unite the city-states. Shortly after he died so Alexander was his heir. Alexander took his father's dream and tried to unite the Greeks, the Persians, and the Macedonians. He failed
He built the Royal Roads
To marry his generals to Persian aristocracy an produce a hybrid ruling class. To introduce Greek-style cities to spread Greek culture. To introduce Greek as the lingua franca.