Alexander did several things to keep his empire united when he was alive. One thing that he did was he used his armies to control the cities under his rule.
He had Greeks and Persians marry.
If you want an answer, try giving listing the choice you are offering.
War and expansion
they fought with other peoples who in their empire.
i don't now you should till me ?
They helped keep the large empire united.
He didn't. It took him ten years to conquer, and then he died. His generals succeeded him, and split the empire up into kingdoms of their own.
Even while his conquests were continuing, Alexander kept his growing empire united in several effective ways. First, he ensured the contentment of his own troops and officers by rewarding them with land and other material wealth, including leadership positions, from the conquered lands. At the same time, he willingly blended his own culture's ideas and values with the same from the cultures that had been conquered, thereby maintaining a majority-level of happiness among the residents, high and low, of the new empire that was coming into being.
This tactic was successful because it helped Alexander's empire by raising the amount of people in his empire, this was because they wanted to keep their beliefs and they wouldn't rebel because of this. *Quote this on Chase Burnham*
Alexander the Great united people through a common culture (Greek), allowing the people to keep their own religion and honoring all the religions of the people he conquered, and adopting parts of the cultures of his conquered territories.
The end of the Persian Empire, for a start, although whether that was a bad thing or not is debatable. And... The warring factions that arose after his death. His empire was torn into pieces and fought over. Much better to have let the Persians keep it, I think.
They did no such thing. The Industrial Revolution spread spontaneously.