In the era of umar sassanid persian empire was wipèd out frm the map of earth, byzantine roman empire was reduced to thrace and balkan n anatolia, while their richest province was syria was coquered in 636 at yarmouk, aleppo, homs and eventualy antioch, roman eastern headquarter, fell to muslims. Muslim armies marched in the heartland of anatolia, jerasalem, egypt coquered in cuming yrz, while muslim armies in east reached the coasts of makran after defeating sassanids in qadisiyah. Alexender defeated darius 3 with well prepared army he inherited 4m his father philip 2nd. He fought with declining power of achemenids . Umar fought two super powers of the time simaltaneously with a tiny army of volunteers. The only man who z equally imp to umar R.A at this time z khalid ibn walid he z the architect of roman n persian defeat.