Notes: "For almost a decade, Alexander the Great and his army swept across Western Asia and into Egypt, defeating King Darius III and the Persians at the battles of River Granicus, Issus and Gaugamela. Next, despite the objections of the loyal army who had been with him since leaving Macedonia in 334 BCE, he turned his attention southward towards India. It was there, in 326 BCE, that he would achieve what many would consider as his last major victory, the Battle of Hydaspes (in modern Pakistan)." Source: Ancient History Encyclopedia. (In the next video, Alexander's forces are in blue. The red circles represent war elephants).
The invasion was brutal. According to the Oxford Classical Dictionary (OCD, 3rd ed. revised), "Alexander moved into India at the invitation of the local dynasts of the Kabul Valley and Punjab. He was nothing loath to reaffirm the traditional Achaemenid [Persian] claims to the Indus lands. Resistance was treated as rebellion, and his progress through Bajaur and Swat was marked by massacre and destruction ... Even the remote rock-fortress of Aornus (Pir-sar) was reduced by siege at the cost of prodigious hardship, to demonstrate that there was no escape from his dominion."
At the time of Alexander's invasion, very little was known about India. According to the OCD, the country "remained a land of fable and wonders; it was believed to lie in the farthest east, yet Indians were confused with Ethiopians." Alexander pushed his army too far when he decided to add India to his already gigantic empire and a mutiny forced him to abandon the effort. He lost a lot of men crossing the Gedrosian desert and finally made it back to Babylon, where he either died from disease or was poisoned.
Alexander's empire quickly fell apart after his death, but his invasion of India increased the West's knowledge of that mysterious country. According to the OCD, "The conquests of Alexander the Great brought more accurate knowledge of NW India as far as the river Hyphasis (Beas) and vague information about the Ganges valley and Sri Lanka; and the voyage of Nearchus [the navarch commanding Alexander's fleet during the return] reopened a sea connection with the Persian Gulf."