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