An established Islamic force is allowed to fight only those enemies who are engaged in fighting it, without committing any sort of aggression!

Verses 190-193 of Chapter 2:

And fight in the way of Allah with those who fight against you but do not commit aggression because Allah does not like aggressors. Fight against them wherever they confront you in combat and drive them out from where they drove you out. Though killing is bad. persecution is worse than killing. Do not fight against them near the Masjid Haram unless they attack you there. And if they attack you first (even in that sacred area), strike them (without any hesitation); this is the due punishment for such disbelievers. If, however, they desist from fighting (you should also do likewise), and know that Allah is Forgiving and Merciful. Go on fighting with them till there is no more a state of tribulation and Allah's way is established instead. Then if they desist from it, there should be no more hostility except against those who had been guilty of cruelty and brutality.(you should also do likewise), and know that Allah is Forgiving and Merciful.

Comments: God allowed the believers to fight under the above conditions only in Medina where an Islamic state was established under the leadership of the last prophet, but not in Mecca where the disbelievers had prevented them from openly spreading the message of God and started torturing them before they had to migrate to Medina.

Spending money for the sake of God is the means of nearness to him!

Verses 97-99 of Chapter 9:

The bedouins are the worst in disbelief and hypocrisy, and more likely to not know the limits which Allah has revealed to His Messenger. And Allah is All-Knower, All-Wise. And of the bedouins there are some who look upon what they spend (in Allah's cause) as a fine and watch for calamities for you, on them be the calamity of evil. And Allah is All-Hearer, All-Knower. And of the bedouins there are some who believe in Allah and the Last Day, and look upon what they spend (in Allah's cause) as means of nearness to Allah, and a cause of receiving the Messenger's invocations. Indeed these (expenditures) are a means of nearness for them. Allah will admit them to His mercy. Certainly Allah is Oft-Forgiving, Most Merciful.

Does God punish the transgressors in this world with their wealth and children?

Verses 84-85 of Chapter 9:

And in future you should never say funeral prayer for anyone from among them; who dies nor stand at his grave, for they have denied Allah and His Messenger and died the while they were transgressors. And let not the abundance of their possessions and children delude you; for Allah wills only to chastise them by means of their possessions and children in this world and let their souls depart while they are still disbelievers.

Why did God permanently set hypocrisy deep in their hearts of some people?

Verses 75-77 of Chapter 9:

There are some among them, who made this covenant with Allah: If He gives us of His bounty, we will disburse charity and lead a righteous life." But when Allah enriched them by His bounty, they grew niggardly and went back on their covenant, and paid no heed to it. As a consequence of the breach of the covenant they had made with Allah and the lies they told, He set hypocrisy deep in their hearts that will follow them till the Day when they shall meet Him.

Why did God disapprove of the exemption granted by the Holy Prophet to the hypocrites from going to fight (with the army of the Roman Empire)?

Verses 43-49 of Chapter 9:

May Allah forgive you. Why did you grant them leave, until those who told the truth were manifest to you, and you had known the liars. Those who believe in Allah and the Last Day, would not ask your leave to be exempted from fighting with their properties and their lives; and Allah is the All-Knower of those who have Taqwa. It is only those who believe not in Allah and the Last Day and whose hearts are in doubt that ask your leave. So in their doubts they waver. And if they had intended to march out, certainly, they would have made some preparation for it; but Allah was averse to their being sent forth, so He made them lag behind, and it was said (to them): "Sit among those who sit (at home).'' Had they marched out with you, they would have added to you nothing except disorder, and they would have hurried about in your midst (spreading corruption) and sowing sedition among you -- and there are some among you who would have listened to them. And Allah is the All-Knower of the wrongdoers. Verily, they had plotted sedition before, and had upset matters for you, until the truth (victory) came and the decree of Allah became manifest though they hated it. And among them is he who says: "Grant me leave and put me not into trial.'' Surely, they have fallen into trial. And verily, Hell is surrounding the disbelievers.