Why do people say, "Alexander the Great conquered the world?"

The ancient historian Justin (one of our main sources for Alexander's life) says this, "As he was returning to Babylon, from the distant shores of the ocean, he was acquainted that embassies from the Carthaginians, and other states of Africa, as well as from the Spains, Sicily, Gaul, and Sardinia, and some also from Italy, were waiting his arrival at that city. So powerfully had the terror of his name diffused itself through the world, that all nations were ready to bow to him as their destined monarch.

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Alexander The Great did NOT conquer the world; that is to say, he did NOT conquer EVERY country, land or peoples living on this planet. What was impressive about Alexander's imperial conquest were the breadth of territories and lands he-(and his fellow Greek soldiers) conquered when beginning his Campaign in a small town in Northern Greece. Alexander's empire encompassed much of present-day Greece, a small portion of the Southern Balkans, Egypt, Asia Minor/Anatolia-(present-day Turkey), the Middle East and much of Central Asia........all of this BEFORE the age of 35 and in less than 20 years.

Although Alexander and his Greek Army did not actually conquer the world, they believed that they came close to conquering the known world. It is very unlikely that Alexander-(and the Ancient Greeks in general) were aware of the existence of native peoples of the Americas. Alexander and the Ancient Greeks would have known very little about the peoples of Africa-(except for Egyptians, Phoenician Carthaginians and Ethiopians). The Ancient Greeks knew about the Germanic and Celtic peoples of Europe, though often viewed them as, "barbarians".

However, much of the continent of Asia-(including China), was very well known (and even admired) by the Ancient Greeks and one must remember that is was the continent of Asia that produced some of the most advanced civilizations during Alexander's time-(including, Greek speaking Asia Minor/Anatolia). The one country which served as the Imperial Epicenter of continental Asian sophistication, advancement and Power during Alexander's time, was Persia-(present-day Iran). For Alexander, the conquest of imperial Persia, was, the conquest of the world.........(West of China).

Alexander the Great conquered what was then the known, "civilized" world.

The four early civilizations were the Egyptian, Babylonian, "Indian" and Chinese. Babylon was part of the Persian Empire, which Alexander defeated. Egypt was conquered next. Shortly before his death, Alexander penetrated to the Indus Valley, which was then the heart of "Indian" civilization based in modern Pakistan and Punjab. Only China was "missing." She was remote from, and (at the time) smaller than the other three civilizations. By the standards of his time, Alexander had conquered the "world" known to him and the Greeks.

The fifth and sixth civilizations were the Greeks and the Romans. Alexander (or rather his father) had conquered the Greeks. When Alexander died in 323 BCE, no one knew that Rome would soon be "the next big thing." At the time, it was just one of the "barbarian" lands to the west. But if Alexander had died a century or two later, he would not have conquered the known "world" unless his conquests included Rome.

Wikipedia tells us that Alexander did indeed set out to conquer the whole world.

His empire consisted of most of the world known to the ancient Greeks of his time, so for his compatriots, yes, he conquered "the world" as they knew it.

As far as empires are concerned, the Macedonian empire is certainly among the greatest empires of all time. With the exception of the Achaemenid empire, any larger empire came after Alexander's time. This includes China (the Qin dynasty doesn't even show up in the list of largest empires -- China's big days were yet to come) and India (the Mauryan empire doesn't reach the size of Alexander's domain either).

All this lends credit to the claim that he conquered "the world".