Right. When Islam was founded, in around 650 AD, Arabic society could be very cruel. As I'm no expert at all on pre-Islamic history, I can tell you fairly little about it, but it is generally accepted that the rise of Islam certainly made life easier for some inhabitants of Arabia. Whereas one was completely dependent on the protection of the clan before the founding of Islam, the Arabian tribes were now also united under a single religion.

Meanwhile, in Persia and Anatolia, the Sassanids and Byzantines had fought eachother nearly to death, so when the Arabian warriors arrived, they pretty much rolled over the Sassanid and Byzantine empires. There was some struggle over Persia, but before long, the Sassanid empire was completely destroyed, while the Byzantines still controlled much of Anatolia.

In any case, whereas Christianity has very little to say about warfare and prisoners of war, etc, the Qur'an is a lot clearer about it:

1) It is illegal to pursue a war after your enemy has surrendered
2) It is illegal to kill prisoners of war
3) It is illegal to harm nature when doing battle

Especially the really orthodox Muslims, people like Salahuddin Ayyubi, who pretty much single-handedly overthrew the Shi'ite Fatimid government of Egypt, abided to these rules. While Islam is not inherently more forgiving than other religions, it has some very specific rules when it comes to fighting other people, especially Jews and Christians (who are defended in the Qur'an as being Ahl al-Kitab (whether the Muslims really abided to this all the time is debatable, especially with the massacre of the Banu Qurayza)). Apart from that, Muhammad also stated that one should "seek knowledge wherever you can, even if you have to travel to China".

This, as well as the fact that Islamic philosophy (as first proposed by Al-Farabi) states that knowledge and reason are not in conflict with religious authority, made the Muslims, when they conquered the Levant and Persia, where science had been practiced for many centuries, quite interested in the workings of the physical world. And thus started what we know as the Islamic Golden Age: through the collection of Sanskrit (which had been brought to Baghdad's House of Wisdom), Greek, Persian, Syriac and Chinese scientifical works and the way this was expanded by Muslim scientists like Omar Khayyam, Al-Khwarizmi, Ibn al-Haytham (Alhazen), ibn Rushd (Averroës), ibn Sina (Avicenna) as well as many others, both Muslim and non-Muslim.

Also, one should understand that mass conversion of non-Muslims didn't start until at least the 10th century; as non-Muslims had to pay the jizya, the Caliphs actually tried not to convert anyone, as that would mean a loss of tax revenue. In the early history of Islam, Islam was exclusively a religion for Arabs; the Ommayad Caliphate was also an Arabic caliphate, ruled by Arabs, for Arabs; which is also one of the biggest reasons for the fact that they were overthrown by the Abbasids, who found quite some support from their Persian subjects.

Also, I'd like to say two things.

1) I'm not Muslim
2) Don't involve modern-day politics in this debate. We are merely looking at Islamic history, not at Islamic theology or at the actions of radical fundamentalist groups in Palestine, Afghanistan or any other place.