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The northwestern part of the South Asia, including Punjab, was repeatedly invaded or conquered by various foreign empires, such as those of Tamerlane, Alexander the Great and Genghis Khan. Having conquered Drangiana, Arachosia, Gedrosia and Seistan in ten days, Alexander crossed the Hindu Kush and was thus fully informed of the magnificence of the country and its riches in gold, gems and pearls. However, Alexander had to encounter and reduce the tribes on the border of Punjab before entering the luxuriant plains. Having taken a northeasterly direction, he marched against the Aspii (mountaineers), who offered vigorous resistance, but were subdued.[citation needed] Alexander then marched through Ghazni, blockaded Magassa, and then marched to Ora and Bazira. Turning to the northeast, Alexander marched to Pucela, the capital of the district now known as Pakhli. He entered Western Punjab, where the ancient city of Nysa (at the site of modern-day Mong) was situated. A coalition was formed against Alexander by the Cathians, the people of Multan, who were very skilful in war. Alexander invested many troops, eventually killing seventeen thousand Cathians in this battle, and the city of Sagala (present-day Sialkot) was razed to the ground. Alexander left Punjab in 326 B.C. and took his army to the heartlands of his empire.[citation needed]

What empires did South Asia invade?
unanswerable