The answer to that is to say this view is erroneous. It is either borne out of sheer ignorance about the Deen of Islam; its conquests, battles and texts. Or borne out of bigotry, and enmity towards the religion.
The truth however is that the religion of Islam rose upon calling with wisdom and beautiful exhortation; Islam promotes and calls to peace, indeed the word salam (peace) is derived from Islam. Whoever ponders over the texts of the Noble Qur'ân and the Purified Sunnah which include the directives of the Messenger of Allâh – SallaLlâhu alahy wa sallam – to the commanders of his army; among that too is the life history of the Messenger of Allâh – SallaLlâhu alahy wa sallam – himself regarding wars; whoever studies all those pertinently, will come to know that Islam came with wisdom, mercy, peace and harmony; it came with making the affairs better not corrupting them.
Read the Word of Allâh the Majestic:
There is no compulsion in religion. Verily, the Right Path has become distinct from the wrong path. [Al-Baqarah: 256].
And this other Word of Allâh:
And had your Lord willed, those on earth would have believed, all of them together. So, will you then compel mankind, until they become believers. [Yûnus: 29].
Allâh the Majestic also said:
Allâh does not forbid you to deal justly and kindly with those who fought not against you on account of religion and did not drive you out of your homes. Verily, Allâh loves those who deal with equity. [Al-Mumtahanah: 8]
He the Majestic still said:
And fight In the Way of Allâh those who fight you, but transgress not the limits [Al-Baqarah: 190].
There are various other Verses of the Qur'ân in this direction.
As for what has come in the Sunnah of the Messenger of Allâh – SallaLlâhu alahy wa sallam –, all the acts of the Prophet – SallaLlâhu alahy wa sallam – in wars and his directives to his army commanders indicate that.
For instance, the Messenger of Allâh – SallaLlâhu alahy wa sallam – said in the hadith of Buraydah (may Allâh be pleased with him) which can be found in Sahîh Muslim that the Messenger of Allâh – SallaLlâhu alahy wa sallam – was such that anytime he wanted to send an army on an expedition, he would exhort its commander to specifically have the fear of Allâh in him, so also he would exhort those who were with the commander. Then he – SallaLlâhu alahy wa sallam – would say:
'Go forth in the Name of Allâh on the path of Allâh, fight those who disbelieve in Allâh, do not steal from the war booty, do not be treacherous (in your treaty with the enemy), do not mutilate (the dead bodies of your enemy), and do not kill children…'
In another narration agreed upon by Al-Bukhaari and Mulsim, the Messenger of Allâh – SallaLlâhu alahy wa sallam – forbade killing of women and children (in battles).
And he – SallaLlâhu alahy wa sallam – said,
'Go forth in the Name of Allâh, fight in the path of Allâh those who disbelieve in Allâh; but do not break the treaty, do not steal from the booty, do not mutilate, do not kill children nor the clergy people in churches.' [recorded in Mushkilu'Aathaar of Al-Imam At-Tahâwee. There is Ibrâhim bn Ismail bn Abee Habîbah Al-Ash'halî in the chain; this fellow is declared weak by Ibn Hajar and Adh-Dhahabee. Perhaps with similar wordings of the hadith in other authentic routes, the hadith can become hasan on the least. – Compiler].
Somewhere else he – SallaLlâhu alahy wa sallam – said,
'Do not kill an elderly person who is close to his death.' [Ash-Shaykh al-Albânee declared the hadith weak in Da'eef Al-Jâmi (1346) and Al-Mishkaat (3956); meanwhile there are similar narrations expressing the purport of the hadith; Allâh knows better. – Compiler].
Abu Bakr As-Sidîq – may Allâh be pleased with him – enjoined upon Yazid bn Abee Sufyân – may Allâh be pleased with both – when he sent him as an army commander to wage war against one-fourth of the Greater Syria, he said to him:
'I counsel you upon ten manners (to be observed in the war): Do not kill women nor children, nor old people; do not cut economic trees of the town nor destroy its dwellings nor slaughter its sheep nor camel, except for consumption; do not drown the date-palm nor burn it; do not steal from the booty and do not act cowardly.' [Mâlik recorded the narration in Al-Muwata' (808).]
Therefore whoever ponders upon the biography of the Messenger of Allâh – SallaLlâhu alahy wa sallam, would come to realize that he never forced anybody to accept Islam; he would only fight whoever fought him, as for whoever entered into a truce with him, he would not fight him so far the latter respected the terms of the truce. In fact, the command of Allâh is that he should respect the terms of any treaty with the unbelievers so far the latter do not break the terms too. Allâh the Majestic said:
So long, as they are true to you, stand you true to them. Verily, Allâh loves Al-Muttaqûn (the pious). [Taubah: 7].
When the Messenger of Allâh – SallaLlâhu alahy wa sallam – arrived in Madeenah, he entered into an agreement of peace with the Jews and allowed them to be upon their religion. When the Jews however waged a war against him (by supporting the unbelievers in Makkah) and broke their treaty, he too fought them in their abodes…
The purpose of the foregoing is that the Messenger of Allâh – SallaLlâhu alahy wa sallam – never forced anybody to embrace Islam, people rather entered Islam out of their own choice. In fact, the bulk of the people on earth entered Islam when the guidance became plain to them that Muhammad was indeed the Messenger of Allâh – SallaLlâhu alahy wa sallam.
[Adapted from the introduction to the Book of Jihâd in Bulûghul-Marâm, pp. 423-425].