The Indian campaign of Alexander the Great began in 326 BC. After conquering the Achaemenid Empire of Persia, the Macedonian king (and now the great king of the Persian Empire), Alexander, launched a campaign into the Indian subcontinent. The rationale for this campaign is usually said to be Alexander's desire to conquer the entire known world, which the Greeks thought ended in India.
After gaining control of the former Achaemenid satrapy of Gandhara, including the city of Taxila, Alexander advanced into Punjab. The Battle of the Hydaspes river against a regional Indian King, Porus, is considered by many as the most costly battle fought by Alexander and his armies. Subsequently, his army refused to cross the Beas River, fearful of the powerful Nanda Empire which lay to the East along the banks of the Ganges. Therefore, Alexander turned south, advancing through southern Punjab and Sindh, along the way conquering more tribes along the lower Indus River, before returning into the west.
Alexander died in Babylon on 10 or 11 June 323 BC. In 321 BC, two years after Alexander's death, Chandragupta Maurya of Magadha founded the Maurya Empire in India.
