Question: It is mentioned in the Qur'an ([9:29](http://quran.com/9/29)) that,

> 
> Fight those who believe not in Allah nor the Last Day, nor hold that forbidden which hath been forbidden by Allah and His Messenger, nor acknowledge the religion of Truth, (even if they are) of the People of the Book, until they pay the Jizya with willing submission, and feel themselves subdued.
> 
> 
> 

Why it is necessary for non-Muslims to pay *Jizya*? Although females, children and the poor are exempted from it I do not find any justification for others.

Please note that Muslims are required to pay *Zakah* but if they do not, there is no punishment for them doing so. But if any non-Muslim refuses to pay the *Jizya* he may lose all of his property, as mentioned in hadith ([Muslim:19:4294](http://www.sunnah.com/urn/242940)):

> 
> If they refuse to accept Islam, demand from them the Jizya. If they agree to pay, accept it from them and hold off your hands. If they refuse to pay the tax, seek Allah's help and fight them.
> 
> 
>

Answer: 
As you rightly mentioned, a similar tax (wouldn't want to use that word because there is no notion of taxation in Islam) had to be paid by Muslims, that is *Zakah*. By paying Jizya, the non-Muslim in a Muslim emirate was both, exempted from compulsory military service *and* was also protected from his enemies. Muslims were accorded no such privilege; Zakah-payer or not, every able-bodied Muslim was liable for military conscription. Secondly, Jizya was liable only upon able-bodied non-Muslim men of military age.

An example of this was during the Muslim ouster from Spain in the 15th century. Since the Muslim rulers could no longer protect people of the Jewish faith from the onslaught of the oncoming Crusaders, they were returned their Jizya amounts.

HTH.
***Treaty of protection*** made by **Khalid Ibn Al-Walid** with the Christians of Al-Hira in Iraq states: 

> 
> Any aged non-Muslim who is unable to earn his livelihood, or is struck by disaster, or who becomes destitute and is helped by the charity of his fellow men will be exempted from the capitation tax and will be supplied with sustenance by the bait al-mal (the government treasury). (Abu Yusuf, Al-Kharaj, p. 144)
> 
> 
> 

The obligation of paying this tax is also canceled when non-Muslims participate with Muslims in defending the Islamic state against its enemies.  

Such conditions were clearly stated in contracts and other documents signed by Muslims and non-Muslims during the reign of **Umar ibn Al Khattab**. (*See Zeidan, 'Abdul Karim, Ahkam- Dhimmiyin Wa Al-Musti'minin Fi Dar Al-Islam, p. 155 ff, and Al-Baladhuri, Futuh Al-Buldan, p. 217*, where it is stated that `the emissary of Abu 'Ubaida made a compromise with a party of the Christian Jarajima: if they would support the Muslims and keep an eye on their enemies, they would not have to pay the Jizyah`) Should the Islamic state become unable to abide by the contract, it may not collect the `Jizyah`.  

This rule was followed by **Abu 'Ubaidah** when he learned of the situation in several Syrian cities. Syria had fallen into the hands of the Muslims, but as the Romans were gathering troops to regain it, he decided not to undertake the protection of the non-Muslims.