Quite literally the simultaneous persecution of heretics by the Byzantines against the Ghassanids and the Persians against the southernmost tribes in their territories opened the highway to Islam. The loot to be gotten did the rest. The Ghassanids simply switched horses.
Islam would today be an obscure tribal religion based solely in the Saudi peninsula, but for Christian persecution.
Basically our own in house fighting always seems to get the best of us. As an example, If Serbia didn't attack Austria over a dispute of Ottomans territory we may not have had WWI or WWII. I doubt Austria would have been able to hold the territory for very long and Serbia could have taken it then.
Philp II attacking England because he didn't get the support he really should have had.
France siding with Germany after being invaded then François Darlan attempting to give the Germans their fleet. In the Battle of Mers-el-Kébir, Battle of Dakar and a few others battles. There were more vichy french volunteers then there were free French forces early in the war. This always amazed me how a country could side with their invaders.
I honestly don't understand any of it.