It’s not. It goes direct to the way Islam spread - by war, and oppression!

You can call pertinent argument a red-herring!
Where exactly does it do that? Habib Ali clearly states the following:
The authoritative and traditional Islamic rules of war can be summarized in the following principles:
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Code:
Non-combatants are not permitted or legitimate targets. This was emphasized explicitly time and again by the Prophet, his Companions, and by the learned tradition since then.
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Religious belief alone does not make anyone the object of attack. The original Muslim community was fighting against pagans who had also expelled them from their homes, persecuted, tortured, and murdered them. Thereafter, the Islamic conquests were political in nature.
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Muslims can and should live peacefully with their neighbors. And if they incline to peace, do thou incline to it; and put thy trust in God (al-Anfal 8:61). However, this does not exclude legitimate self-defense and maintenance of sovereignty.
How on earth can that letter go directly to the issue of Islam spreading by war? By the fact that it allows standing up against oppression and injustice?
So Christians had previously been taxed by Christians? What is it you’re saying here?
What I’m saying is this, and that is if you want to know why Islam spread as far and wide as it did through Christian communities then you need to examine the conditions prevailing among the people of the time, where there still existed tribal communities often at war with one another, and Islam seemed a unifying force to them. People seem to think that just because there exists an antogism between some Christians and Muslims these days, this was always the case, however it is far from true. For exmaple, after the battle of Qadisiyya (14 AH) after the victory of the Muslims over the Persian army (under Rustam), many Christians belonging to the Beduin tribes on both sides of the Euphrates came to the Musim general and said, “The tribes that at the first embraced Islam were wiser than we. Now that Rustam hath been slain, we will accept the new belief” (see Muir’s Caliphate, pp 121-2). Similarly in northern Syria, most of the Christian Beduin tribes joined themselves to the followers of the Prophet (Caetani, vol iii p 814). Yes, Muslims were involved in battles at the time involving the “sword”, however conversion to Islam was not the motive as is often made out.
Or, for example, the battle of the Bridge (13AH) where a disasterous defeat was imminent for the Muslims, who were hemmed in between the Euphrates and the Persians, were saved when the Christian chief of Banu Tayy sprang forward to the side of the Muslims to assist them in an orderly retreat. When the enemies of the Muslims stepped up their campain to prevent this, the Christian tribes of Banu Namir and Banu Taghlib turned up and helped the Muslims and turned the battle in their favour.
Bani Taghlib remained a Christian tribe for some time, and were never pressured to abandon their old faith and it was ordered by the Caliph Umar r.a. that they should be left undisturbed in the practice of it.
In fact they were called upon to pay the jizyah but opposed it as they felt it to be humiliating to their pride to pay a tax that was levied in return for their protection, and petitioned the Caliph who then reduced the jizyah to the same amount as that payed by the Muslims, the 2.5% I mentioned.
The tolerance extended by the victorious Muslims of the first century after Hijrah infers that those that did convert did so out of their own choice and free will. The fact that there are still Christian Arabs living today amongst the Muslim is tesatment that the “convert or die” attitude is merely a myth. If it was the case, Greece could never have remained a Christian country after being ruled by the Ottomans for over 500 years.
And you’re mixing up the jizyah (10%) imposed on non-believers with zakat (2.5%) imposed on believers!
The mere fact that they impose a higher tax on non-believers is ‘compelling’
Please… the jiziyah was imposed only on men as an exemption for having to fight to protect the nation, and which cannot be extracted by force. In some cases, non-Muslims forewent the payment and fought amongst the Muslims. Compare this to the zakat payable by every Muslim, man, woman and child, on their wealth, their livestock, their crops (up to 10%), etc.
Or take, for example, the writings of Michael the Elder, Jacobite Patriarch or Antioch, writing in the latter half of the twelth century after five centuries of Muslim rule, where after recounting the persecutions of Heraclius, writes:
“This is why the God of vengeance, who alone is all powerful, and changes the empire of mortals as He will, giving it to whomsoever he will, and uplifting the humble - beholding the wickedness of the Romans who, throughout their dominions, cruelly plundered our churches and our monasteries and condemned us without pity - brought from the region of the south the Sons of Ishmael, to deliver us through them from the hands of the Romans. And, if in truth, we have suffered some loss, because the Catholic churches, that had been taken away from us and given to the Chalcedonians, remained in their possession; for when the cities submitted to the Arabs, they assigned to each denomination the churches which they found it to be in possession of (and at the time of the great church of Emessa and that of Harran had been taken away from us); nevertheless it was no slight advantage for us to be delivered from the cruelty of the Romans, their wickedness, their wrath and cruel zeal against us, a
nd to find ourselves at peace” (see Micheal the Elder, vol. ii pp 412-413).
When the Muslim army reached the valley of the Jordan and Abu Ubaydah pitched his camp at Fihl, the Christian inhabitants of the country wrote to the Arabs and said, “O Muslims, we prefer you to the Byzantines, though they are of our own faith, because you keep better faith with us and are more merciful to us and refrain from doing us injustice and your rule over us is better than theirs, for they have robbed us of our goods and our homes” (Azdi, p 97).
The people of Emessa closed the gates of their city against the army of Heraclius and told the Muslims that they preferred their government and justice to the injustice and oppression of the Greeks. (Baladhuri p137).
A similar thing happened in Syria against the Romans in 644-649 when the Arabs drove them out. And again in Damascus in 637, as well as Emessa, Arethusa, Hieropolis and even Jerusalem. The fear of religious compulsion
on the part of the heretical emperor was what made the promise of Muslim toleration appear more attractive to them - not the other way around as is often asserted.
For example, when Jerusalem submitted to Caliph Umar, the following conditions were drawn up:
“In the name of God, the Merciful, the Compassionite! This is the security which 'Umar, the servant of God, the commander of the faithful, grants to the people of Aelia. He grants to all, whether sick or sound, security for their lives, their possessions, their churches and their crosses, and for all that concerns their religion. Their churches shall not be changed into dwelling places, nor destroyed, neither shall they nor their appurtenacnes be in any way diminshed, nor the crosses , and for all that concerns their religion. THeir chuches shall not be changed into dwelling places, nor destroyed, neither shall they nor their appurtenances be in any way diminished, nor the crosses of the inhabitants nor aught of their of their possessions, nor shall any constraint be put upon them in the matter of their faith, nor shall any one of them be harmed”. (Tabari i. p 2405).
I could continue on with many, many more examples, and I apologise for the length of the post so far, however I think it’s important to realise that the picture being portrayed of the spread of Islam by many people today, out of ignorance as I claim, is far, far from the truth. Nothing personal, but there are many of these accounts to be found in history and whilst I fully admit things were not always so rosy, they amount to a minority of cases compared to the norm, which was tolerance.