How did alexander unify his empire?

Alexander, is referred to as the Great, for a reason. He obviously was the driving force of Greece. He helped to make his father's dream of conquering Greece and defeating Persia a reality. He and his father introduced new military methods to the Greeks including the battering ram, catapult, new battle formations and the use of an infantry and calvary. He encouraged his men to fight and they willing fought alongside him.

Hope I helped :) 

A) the gas is compressed