The contributions of Alexander the Great to the idea of empire and empire building cannot be underestimated. It is generally agreed that Alexander the Great was the founder of the first global empire in World History. The more profitable question is how Alexander the Great achieved such a feat.
The most telling feature of Alexander the Great's outlook on empire building was the importance of cosmopolitanism to the maintenance of an expansive empire. Alexander realized the impracticality of ruling very diverse groups of people from Southern Europe to Egypt to India and Central Asia by enforcing a uniform cultural standard. He concluded that subjects of his empire, while they must demonstrate allegiance to him, should have the ability to retain the various aspects of their own cultures.
Alexander the Great, however, did not stop at the simple realization that he ruled numerous different peoples with different customs and cultures; in the government of his empire, he encouraged his territorial officials to intermarry with the local population. Alexander understood that it was crucial to establish a connection between the incoming conquerors and the conquered. Doing so established a rapport between the two sides and actually encouraged effective government, while discouraging the temptations of tyrannical behavior.
This practice of intermarriage between officials and the local populations actually contributed to Alexander the Great's ideas about governing such an empire. After Alexander the Great died in 323 B.C.E., his view of empire allowed for a reasonably smooth transition. The areas of his empire already under the control of his generals - Ptolemy (Egypt), Seleucus (Babylon), Antigonus (India and the east) - did not significantly change in the way they were governed.
Empire builders who followed Alexander the Great continued to look at his campaigns and government models as indicators of how to rule an expansive empire effectively. The influence of Alexander the Great's empire building and cosmopolitan outlook on the leaders who followed him - the Romans and Napoleon among others - provide the most compelling evidence for his contribution to the idea of empires and empire building.