And what do you think woud've happened if they couldn't pay the Jizya tax?
No doubt that it was enforced to compensate Muslims for their losses, but didn't the Muslims raid caravans in order to gain goods and compensate themselves? This is stealing, so Muhammad broke a Koranic rule?
Jizya was also a protection racket ala Al Capone stylee.
He accepted rewards in the flesh (what was that Jewess called again?) and was entitled to spoils of war.
I think you are refering to the term "ma malakat aymanukum" in the Quran which in English means "whom you right hand possess". The Islamic sects interpret that whom you possesses as slaves. Actually this term means concubine. A concubine is any women a man posseses by oah wothout dowry. It is a Biblical term common in Judaic traditions. Many prophets in the Bible had concubines. It has nothing to do with slavery. What is even more unusual is the Islamic sects applied it usually with captives of war, probably a Meccan tradition.
The Quran only allowed two options for prisoners of war. Freedom or ransom. The verses about MMA has nothing to do with prisoners of war.
As far as MMA is concerned, MMA is what we call a concubine. Many prophets in the Old Testament had concubines as well as wives.
The only difference is concubines have no dowry arrangements and is considered an inferior form of marriage for that reason. When the believers came to Medina they came across a larger Jewish presense there and the practice of concubinage (urfi marriage in Arabic) was prevalent. Its an acceptable form of arrangement but the Quran does not advice that form of relationship since its open for abuse.
Later Islamic authorities changed its meaning to mean prisoners of war.
In the Bible
Among the Israelites, men commonly acknowledged their concubines, and such women enjoyed the same rights in the house as legitimate wives.
The concubine may not have commanded the same respect and inviolability as the wife. In the Levitical rules on sexual relations, the Hebrew word that is commonly translated as "wife" is distinct from the Hebrew word that means "concubine". However, on at least one other occasion the term is used to refer to a woman who is not a wife - specifically, the handmaiden of Jacob's wife. In the Levitical code, sexual intercourse between a man and a wife of a different man was forbidden and punishable by death for both persons involved. The Bible notes several incidents of intercourse between a man and another man's concubine, and (rape excepted) none of them resulted in capital punishment for either party, although the man to whom the concubine belonged was dishonored by such a relationship. For instance, Jacob is dishonoured when his son Reuben sleeps with his concubine Bilhah  but the consequence is that Reuben is disgraced and cut out of the genealogical line. David is portrayed as having been dishonored when his son Absalom deliberately has public sex with all his father's concubines on the roof of the palace, on the advice of David's former counsellor Ahithophel. Absalom does this not just as an act of sexual potency but to show the nation that everything David had is now his, that he is the king and in total command and that David is disgraced, exiled and not coming back.
Because it was regarded as the highest blessing to have many children, legitimate wives often gave their maids to their husbands to atone, at least in part, if they were barren, as in the cases of Sarah and Hagar, and Rachel and Bilhah. The children of the concubine often had equal rights with those of the legitimate wife; for example, King Abimelech was the son of Gideon and his concubine. However, Abraham's actions in allowing his wife Sarah to drive his concubine Hagar away and in sending all the sons of his concubines away with gifts, rather than allowing them to stay and have an equal inheritance with his son Isaac, indicates that he saw them as inferior to Isaac, who had been promised to him and was Sarah's child. Later biblical figures such as Gideon, and Solomon had concubines in addition to many childbearing wives. For example, the Books of Kings say that Solomon had 700 wives and 300 concubines.
The disturbing account of the unnamed Levite  shows that the taking of concubines was not the exclusive preserve of Kings or patriarchs in Israel during the time of the Judges and that the rape of a concubine was completely unacceptable to the Israelite nation and led to a civil war. In the story, the Levite appears to be an ordinary member of the tribe dedicated to the worship of God, who was undoubtedly dishonoured both by the unfaithfulness of his concubine and her abandonment of him. However, after four months, he decides to follow her back to her family home to persuade her to return to him. Her father seeks to delay his return and he does not leave early enough to make the return journey in a single day. The hospitality he is offered at Gibeah, the way in which his host's daughter is offered to the townsmen and the circumstances of his concubine's death at their hands describe a lawless time where visitors are both welcomed and threatened in equal measure. The most disturbing aspect of this account is that both the Levite and his (male) host seek to protect themselves by offering their womenfolk to their aggressors for sex, in exchange for their own safety. The Levite acts in a way which indicates that he believes that the multiple rape of his unfaithful concubine is preferable to the violation of the virginity of his host's daughter or a sexual assault on his own person. In the morning, the Levite appears to be quite indifferent to the condition of his concubine and expects her to resume the journey but she is dead. He dismembers her body and distributes her (body parts) throughout the nation of Israel as a terrible message. This outrages and revolts the Israelite tribesmen who then wreak total retribution on the men of Gibeah and the surrounding tribe of Benjamin when they support them, killing them without mercy and burning all their towns. The inhabitants of (the town of) Jabesh Gilead are then slaughtered as a punishment for not joining the eleven tribes in their war against the Benjamites and their four hundred unmarried daughters given in forced marriage to the six hundred Benjamite survivors. Finally, the two hundred Benjamite survivors who still have no wives are granted a mass marriage by abduction by the other tribes.
There are no concubines in the New Testament. St Paul emphasises that church leaders should be in monogamous marriages, that believers should not have sexual relationships outside marriage. and that unmarried believers should be celibate. Marriage is to reflect the exclusive relationship between the husband (Christ) and wife (his church), described as a "mystery".
In Judaism, concubines are referred to by the Hebrew term pilegesh. The term is a non-Hebrew, non-Semitic loanword derived from the Greek word, pallakis, Greek παλλακίς, meaning "a mistress staying in house".
According to the Babylonian Talmud, the difference between a concubine and a full wife was that the latter received a marriage contract (Hebrew:ketubah) and her marriage (nissu'in) was preceded by a formal betrothal (erusin). Neither was the case for a concubine. One opinion in the Jerusalem Talmud argues that the concubine should also receive a marriage contract, but without a clause specifying a divorce settlement.
Certain Jewish thinkers, such as Maimonides, believed that concubines were strictly reserved for kings, and thus that a commoner may not have a concubine. Indeed, such thinkers argued that commoners may not engage in any type of sexual relations outside of a marriage.
Maimonides was not the first Jewish thinker to criticise concubinage. For example, Leviticus Rabbah severely condemns the custom. Other Jewish thinkers, such as Nahmanides, Samuel ben Uri Shraga Phoebus, and Jacob Emden, strongly objected to the idea that concubines should be forbidden.http://en.wikipedia.org/wiki/Concubinage
Its important to understand that MMA is primarily a Judaic tradition. Western societies understood concubinage differently. Only Islamic authorities attached it to slavery and prisoners of war. But what is important is the Quranic use of the term which is based on its biblical understanding.
When the Quran says "ma malakat aymanukum" meaning what you possessed by oath, it means a relationship established by oath only without dowry or financial arrangement and encourages to elevate that arrangement to a full marriage by establishing a dowry and financial arrangement and also informing family members. This happens many times in urfi marriages where the man denies ever having relationship with a women and tears off the contract he had with her.
Nikah 'urfi is a "customary" Sunni Muslim marriage contract that is not registered with state authorities. This form of marriage usually requires witnesses. Couples repeat the words, "We got married" and pledge commitment before God, although there are many other informal ways in which people marry `urfi. Usually a paper, stating that the two are married, is written and at least two witnesses sign it, although others may record their commitment on a cassette tape and use other forms of documentation. Most Arab countries do not recognize 'Urfi marriages and do not allow partners to get a 'legal' divorce since the government does not recognize the legality of the marriage in the first place. Sometimes these relationships are a way for people to have sex with each other within what is perceived to be a licit framework. Nevertheless, the relationship is often kept secret from family members and women often become pregnant but are unable to prove they are married or get a divorce.
The 'Urfi marriage has always existed, but for different reasons.
In the past, it was common among the widows of soldiers who had huge pensions and they did not want to lose it by officially re-marrying. Now, however, it is mostly among university students and young couples who cannot afford the high cost of marriage.
Undocumented 'Urfi marriages are increasingly popular among Egyptian youth. The high cost of marriage forces many young couples to wait several years before they marry. Conservative Egyptian society forbids sex before marriage, so many young people consider the 'Urfi marriage a solution. 'Urfi marriages are conducted by a Muslim cleric in the presence of two witnesses. However, they are not officially registered and are not legally financially binding on the man. Couples married in this way often meet in secret and avoid the expense of renting an apartment. The 'Urfi marriage can be disastrous for the wife in legal terms. If the husband leaves her without granting her a divorce, she had no legal right to seek a divorce since 'Urfi marriage is considered illegal. Her husband could remarry. The wife is in a more difficult position. If the wife remarries, she can be accused of polyandry, which is punishable by seven years in prison in Egypt, or she could remain single for the rest of her life.
The new Egyptian law (passed in 2000) recognizes the woman's right to seek divorce from an 'Urfi marriage. However, the law denies her alimony and child support.
There are also controversial, unofficial "'Urfi" marriages, where a couple signs documents declaring themselves married. The couple does not inform their families of the marriage. Many Egyptian clerics are against this type of 'Urfi marriage calling it a cover for pre-marital sex.
An extreme form of 'Urfi marriage is known as zawag al-'urfi: to give prostitution an Islamic cover, some women enter into secret marriage contracts with their summer visitors. Known in Egypt as zawag al-'urfi, this contract is made without witnesses and typically ends in divorce by summer's end. Most of Egypt's Islamic scholars condemn this use of zawag al-'urfi.http://en.wikipedia.org/wiki/Nikah_%27urfi
It has nothing to do with slavery or prisoners of war. Slavery is a barbaric act practiced by the Pharaoh in the Quran and Joseph's brothers and sex with female slaves is rape and nothing else and prisoners of war are already discussed in the Quran.