How and why did Alexander the Great create an empire, and what was its political legacy?

Fully intending to carry out Philip’s designs to lead the Greeks against the Persians, Alexander (r. 336–323 B.C.E.) proclaimed to the Greek world that the invasion of Persia was to be a mighty act of revenge for Xerxes’s invasion of Greece in 480 B.C.E. and more recent Persian interference in Greek affairs. Although he could not foresee this, Alexander’s invasion ended up being much more. His campaign swept away the Persian Empire, which had ruled the area for over two hundred years. In its place Alexander established a Macedonian monarchy, and although his rule over these vast territories was never consolidated due to his premature death, he left behind a legacy of political and cultural influence, and a long period of war. Macedonian kings established dynasties and Greek culture spread in this Hellenistic era.