It was Muhammad and the Muslims who were subject to barbaric treatment for 13 years once they began teaching there was only one God.
I doubt very much the Meccans did as much harm as you think. Muhammad was under the protection of a very powerful uncle (as indicated in the ahadith) which is why the persecution went on as long as it did - as opposed to the Meccans stopping Muhammad right away. Also; they didn't persecute him simply because he preached the worship of one god. Christians & Zoroastrians were welcome in pre-Islamic Mecca, after all. What the Meccans took exception too was Muhammad's habit of slandering their gods & beliefs (and by extension their ancestors who believed in those gods) as false - as well as baselessly claiming their main temple for his own upstart faith. In those days attacking the religion of a people was one of the most insidious ways to undermine their identity; it was much the same with the Romans & the Greeks.
Now imagine me, a non-Muslim, trying to slander Islam in Mecca today. I wouldn't last thirteen seconds, never mind thirteen years. For all these claims that the Quraysh were intolerant, they didn't bar the city to everyone who didn't share their religious views.
The Meccans murdered Muslim women and tortured and killed many Muslims when they refused to give up belief in one God.
I suspect if they were killed it would probably have been more to dissuade people from following Muhammad's example of undermining the identity of their own city. That said, I'm certain there was a fair amount of 'he's a treat to our power & prestige' motive in there too.
That’s all there was to it. It was vile, cruel religious persecution.
Issues are rarely that simple. Because they're the victors we've only ever heard Muslim accounts of the story so I'm certain there's more to this thing than we're being told.
After Abyssinia the Muslims went to Medina where there was a dispute between the ruling tribes and as Muhammad was able to reconcile them, they chose Him as their new leader and accepted Islam voluntarily.
This is partially true at best. Medina probably accepted Muhammad's leadership partly because he was the relative of the influential Banu Quraysh of Mecca, and partly because he was the latest strongman to show up with his own warband. On the subject of accepting Islam, the Banu Qurayza, by Muslim accounts, did not convert to Islam; indeed they would have rejected Muhammad's claim to being a prophet of their god as he was not a Jew. This is possibly the main cause of Muhammad's enmity towards them and
the resulting mass-murder of their tribe's entire adult male population at his order; though naturally
it was apparently ordered by Allah.
The Meccans sent out spies and were hunting Muslims with intent to commit genocide and wipe them out completely.
Muhammad had Medina protected but the Meccans were always close by trying to find ways to murder and kill the Muslims. It was a war by the Meccans against religious freedom.
You make it sound as though the Quraysh were completely unprovoked which doesn't even match with what Muslims have to say on the matter. The real reason the Quraysh were after Muhammad is his followers had started raiding their trade caravans - further threatening their power, wealth and the prosperity of Mecca.
The early Muslims were, in effect, bandits, highwaymen and thieves (link is to an Islamic scholarly interpretation that says once they gained political power it was acceptable for Muslims to start attacking others).
Muhammad never killed a soul. His character was impeccable.
He ordered the fighting-age men of the Banu Qurayza tribe of Jews to be put to the sword while the women and children were made slaves. If a leader gives an order to kill he is as culpable as the ones who did the deed. The truth is Muhammad's conduct in the matter was no different than any other barbarian warlord of the age.
