The Battle Of Qadisiyyah

The victory of Qadisiyyah heralded the downfall of the Sasanian Dynasty, paved the way for the conquest of Iraq and quickened Islamic expansion into Persia (Iran) and beyond. The Iranians had 240,000 troops, but the Muslims with about 30,000 soldiers still drove the Iranian Empire, one of the superpowers of the day, into the ground.
At Al-Qadisiyyah, the Muslims were able to break the Persian might, dealing them a blow from which they would never recover. The Battle of Al-Qadisiyyah is therefore one of the most decisive battles in the history of humanity.