Allah himself is fighting the unbelievers (9:30), why should Muslims no longer fight in his cause as in the cause of evil (4:76)? About 19% of the Quran devote themselves to the violent conquest and subjugation of non-Muslims:
And make ready against them all you can of power, including steeds of war (tanks, planes, missiles, artillery, etc.) to threaten the enemy of Allah and your enemy, and others besides whom, you may not know but whom Allah does know. And whatever you shall spend in the Cause of Allah shall be repaid unto you, and you shall not be treated unjustly. (8:60)
O Prophet (Muhammad)! Strive hard against the disbelievers and the hypocrites, and be severe against them, their abode will be Hell, and worst indeed is that destination. (66:9 - see also 9:73)
Muslims expect a reward in this life as well as in the next one (4:134), so it makes sense that even in this life unbelievers are getting punished:
Is then He (Allah) Who takes charge (guards, maintains, provides, etc.) of every person and knows all that he has earned (like any other deities who know nothing)? Yet they ascribe partners to Allah. Say: "Name them! Is it that you will inform Him of something He knows not in the earth or is it (just) a show of false words." Nay! To those who disbelieve, their plotting is made fairseeming, and they have been hindered from the Right Path, and whom Allah sends astray, for him, there is no guide. (13:33)
For them is a torment in the life of this world, and certainly, harder is the torment of the Hereafter. And they have no protector against Allah. (13:34)
There are at least two places in the Quran, where the violent death of non-Muslims is designated as Allah's reward for unbelief (2:191, 9:26), as in "that is the reward for unbelievers." Verse 3:56 states that "those who reject faith" are punished with terrible torment in this world (a vow that Muhammad and his companions took personally to fulfill).
The Quran tells Muslims that Allah uses them to severely punish others:
Fight against them so that Allah will punish them by your hands and disgrace them and give you victory over them and heal the breasts of a believing people, (9:14)
Verse 4:102, says that Allah has prepared a humiliating torment for the unbelievers. Stories from Muhammad's life show only minor differences between the punishment of Allah and the violence from the hands of faithful Muslims.
Allah can kill unbelievers by himself, but he makes it a test for Muslims to prove their faith:
So, when you meet (in fight Jihad in Allah's Cause), those who disbelieve smite at their necks till when you have killed and wounded many of them, then bind a bond firmly (on them, i.e. take them as captives). Thereafter (is the time) either for generosity (i.e. free them without ransom), or ransom (according to what benefits Islam), until the war lays down its burden. Thus [you are ordered by Allah to continue in carrying out Jihad against the disbelievers till they embrace Islam (i.e. are saved from the punishment in the Hell-fire) or at least come under your protection], but if it had been Allah's Will, He Himself could certainly have punished them (without you). But (He lets you fight), in order to test you, some with others. But those who are killed in the Way of Allah, He will never let their deeds be lost, (47:4)
One of the most brutal chapters in the Quran makes Muhammad and his followers to the "superior over all religions" (9:33).
Verse 8:55 compares unbelievers with animals. In line with this issue, this passage encourages the Muslims to win over them "dominance" and severely punish and intimidate the rest:
So if you gain the mastery over them in war, punish them severely in order to disperse those who are behind them, so that they may learn a lesson. (8:57)
At the end, all beings in heaven and on earth will be compelled to bow down in front of Allah, either willingly or by force:
And unto Allah (Alone) falls in prostration whoever is in the heavens and the earth, willingly or unwillingly, and so do their shadows in the mornings and in the afternoons. (13:15)
Muslims are told that "Allah loves those who fight in his own way" that Islam is "victorious over all other religions", even though the unbelievers resist (61:4-11). Those who resist against the Islam will get humbled:
Those who oppose Allah and His Messenger (Muhammad), they will be among the lowest (most humiliated). (58:20 - The context for this verse is the expulsion of the Jewish tribes from Medina and the confiscation of their wealth, land and children by Muhammad)
Non-Muslims are to be fought until all religion is only for Allah:
And fight them until there is no more Fitnah (disbelief and polytheism: i.e. worshipping others besides Allah) and the religion (worship) will all be for Allah Alone [in the whole of the world ]. But if they cease (worshipping others besides Allah), then certainly, Allah is All-Seer of what they do. (8:39 - Some translate the word "fitna" as "persecution," but in this context it means resistance to Islam - in the predecessor version as unwillingness to believe [cf verse 8:38]. This passage was "revealed" after a battle that deliberately provoked by Muhammad. Verse 2:193 essentially says the same, and was also "revealed" at a time when the Muslims were not under physical attack).
Those with "sick hearts," including Christians and Jews according to verse 5:52, are said to be "slaughtered" (33:60-2) along with the "hypocrites" (Muslims, who cannot get judged as true believers for their associations with unbelievers or their unwillingness), or should engage themselves in jihad.
Non-Muslims are to be attacked, set under pressure and punished by the Muslims
See they not that We gradually reduce the land (of disbelievers, by giving it to the believers, in war victories) from its outlying borders. And Allah judges, there is none to put back His Judgement and He is Swift at reckoning.. (13:41 see also 21:44)
Then leave Me alone with such as reject this Message: by degrees shall We punish them from directions they perceive not. (68:44)
And He caused you to inherit their lands, and their houses, and their riches, and a land which you had not trodden (before). And Allah is Able to do all things. (33:27 - see also Bukhari 53:392)
Allah will grant the Muslims power and authority over all other humans:
Allah has promised those among you who believe, and do righteous good deeds, that He will certainly grant them succession to (the present rulers) in the earth, as He granted it to those before them, and that He will grant them the authority to practise their religion, that which He has chosen for them (i.e. Islam). And He will surely give them in exchange a safe security after their fear (provided) they (believers) worship Me and do not associate anything (in worship) with Me. But whoever disbelieved after this, they are the Fasiqun (rebellious, disobedient to Allah). (24:55)
Muhammad's companion continued this prophecy with an aggressive and senseless military expansion that left a trace of the dead from Spain through North Africa to India.
Allah gives the Muslims instructions for dealing with unbelievers who are not willing to accept Islamic rules:
(Remember) when your Lord inspired the angels, "Verily, I am with you, so keep firm those who have believed. I will cast terror into the hearts of those who have disbelieved, so strike them over the necks, and smite over all their fingers and toes." (8:12)
This is because they defied and disobeyed Allah and His Messenger. And whoever defies and disobeys Allah and His Messenger, then verily, Allah is Severe in punishment. (8:13)
To defeat Non-Muslims should be easy for true believers because they are superior in intelligence and understanding:
O Prophet (Muhammad)! Urge the believers to fight. If there are twenty steadfast persons amongst you, they will overcome two hundred, and if there be a hundred steadfast persons they will overcome a thousand of those who disbelieve, because they (the disbelievers) are people who do not understand. (8:65)
Well, with the intelligence of the Muslims it should not be far. They are so intelligent that they cannot life together. In addition, they may be so busy with praying that there is no time left for other things in life. One can see also the amount of the inventions of the last 1400 years, in which Muslims have been involved, how intelligent the Muslims are.
Remember that the Quran teaches that not all people are equal to Islam. This also applies to Muslims with regard to their aggressiveness towards the unbelievers. Those who are killed or killed in the name of Islam rejoice Allah more:
Not equal are those of the believers who sit (at home), except those who are disabled (by injury or are blind or lame, etc.), and those who strive hard and fight in the Cause of Allah with their wealth and their lives. Allah has preferred in grades those who strive hard and fight with their wealth and their lives above those who sit (at home). Unto each, Allah has promised good (Paradise), but Allah has preferred those who strive hard and fight, above those who sit (at home) by a huge reward; (4:95)