The comparison of Christianity, Judaism and Islam is a very obvious one, because they are closely related to each other. They are the so-called "Abrahamic" religions and foot on the Old Testament. In general, the three religions have three prophets that distinct them from each other. Moses is the prophet of Judaism (although he is also a prophet of Christianity and Islam); Jesus is the prophet of Christianity and Muhammad the prophet of Islam.
Christianity started out as a sect of Judaism stating that Jesus is the promised Messiah all Jews were waiting for. Those who remained Jews rejected this, and are still waiting for the Messiah. The difficulty of uniting Christianity and Judaism therefore arises from the fact that the Jews do not accept the words of Jesus to be of divine nature, which the Christians (or at least most of them) do. To simplify it, the Jews regard the Ten Commandments and the morals of the Old Testament the laws of God. The Christians add the words of Jesus, found in the New Testament, to these old laws.
Islam is, if you will, an "updated" version of Christianity (which is an "updated" version of Judaism). It must be said that the Muslims believe in the divine nature of Jesus Christ, they accept him as a prophet of God, but they believe the Qur'an to be rules that add up to what the Old and New Testaments say. In general, the relation of Islam to Christianity is the same as that of Christianity to Judaism.
In that sense, Judaism, Christianity and Islam are three branches of the same roots. It must be said that in different stages of their developments, they also took different influences from other religions. For example, Christianity uses several concepts that originated in the Persian Zoroastrian religion (which is only natural, considering that in the time Christianity arose, the areas of worship of the two were very close together, neighbouring, in fact). On the other hand, Zoroastrianism also had elements that resembled Jewish ones. For example, in Zoroastrianism, God does not manifestate himself. In his place, the eternal fire was worshipped. It is argued that the symbol for the highest God (Ahura Mazda) shown on ancient Persian bas-reliefs was in fact not intended to be the God, but in fact the ancestors of the Great King receiving their blessing.
One fundamental influence Zoroastrianism had in the development in Christianity was the sharing of Manichaean ideals. Zoroastrianism believes in the eternal struggle between the good God, Ahura Mazda, and his evil adversary, Angra Maniyu (aka Ahriman), which concludes at the end of all times. This led to the development of Manichaean philosophy in the 3d century. Manichaeism believes in the dualism of good and evil. This basically means that there is "black" and "white", but no grey. Although Persian authorities attempted to stop Mani's words from spreading (mostly for political reasons), they did survive and later became the fundament of many Christian theories (the most famous ones in history being those of the Cathars). Manichaeism has survived until this day. One of the most prominent advocates of Manichaeism (although I personally doubt he knows of that) is a certain megalomanic person believed to be destined to rule the world. You all know this person, his Manichaean views were manifestated by the tragically famous words "Either you are with us, or you are against us".
However, if you believe that Christianity is a unified religion, which worships only one God and his prophet, you are gravely mistaken. Christianity had incredible struggles in finding followers in a world that has been Polytheistic for several millenia. For this reason, concepts such as the saints, which were basically just Gods in replacement, were highly successful. The Germanic tribes would have none of Jesus' divinity and accepted the idea of Arianism, which said that Jesus was not the son of God, nor was he divine, but simply a very godly human. During the time Christianity was banned in the Roman Empire, many mixed religions existed which sort of accepted Jesus, but would not entirely dismiss the "Old Gods", as they were known. Finally, Iulianus Apostata created a form of Paganism that was Christian in almost every resort, except for the fact that the divinities worshipped to were not Jesus and his father, but the Old Gods. In describing the various forms of Christianity, one could go on for ages, so I leave you with this basic impression (just to note that I'm not going to start on the subject of Reformation and the term "church").
As for Hinduism, we have a very difficult case here. This begins with the fact that there is no "Hinduistic" religion. The term "Hinduism" was coined by the British overlords to comprehend all those various cults on the Indian subcontinent that were related to each other and seemed to be similar. A compromise was found in the fact that there is a supreme God, but he can take up to 33 million incarnations. These incarnations include characters such as Jesus or Muhammad, indicating that we are in fact all Hindus.
Fact is, however, that this religion is (or at least was up to British rule) non-existent. All the concepts that make up the British definition of Hinduism were there, but not in that shape. There were and still are many different cults that often resemble each other closely. But just to give you an example, a person worshipping Kali is unlikely to worship Ganesh, and so on (this example is flawed, and there are certainly people who do both, and there may be mix cults. I'm not an expert on Hinduism).
The lack of the missionary element in Hinduism does not mean Hindus and other religions can get along with each other. It is not only the other religions that pick up fight with Hindus, but often enough Hindus themselves. The fact is that "modern" Hinduism is also closely alligned to the Indian nation ("Hindu" is in fact just a name for "India" -although the country is officially called Bharat, meaning "mother"), and other religions, mostly Islam, which made a violent entrance on the subcontinent, are considered an alien element in this nation. 1,100 years after the Muslims entered India, many Hindu nationalists still do not consider Indian Muslims to be real Indians. This was one of the main reasons why a country like Pakistan came into existance.
So, it is not always the spiritual or religious factors that make up the clash of religions. If you look at Islam, it radically conflicts with the other two Abrahamic religions not because they consider Muhammad the prophet, but because Qur'an and Hadith were not written for urbanized societies, but were in fact originally the laws the Arabs lived by. The big problem with religions is that once a divine word is written down, it remains unaltered forever. Can the laws of a merchant city in 7th century Arabia be applied to a modern metropolis? Similarities exist, but the times have simply changed.
It would be wrong to dismiss religions as utter bullshit though. Even if you do not believe in God, you must not deny that Christianity is the basis of the western culture. Our set of morales and ethics derives from Christian values, and our society takes as much from its beliefs, past or present, as it takes from other pieces of history, culture and the likes. The figures of good and evil that derive from the Bible and beyond are still present in our minds. Biblical and religious imagery, as secular as it may have become, is still the most powerful imagery in our civilization. We may dismiss the existence of divinity, but none of us are as un-religious as we want to think. The Islamic world has adopted a different, in their view more advanced, set of morales and rules. This is the reason why our cultures clash so often.
Finally, the problem of religion lies not within the individual, but in the mass as a whole. Any person you talk to will be more intelligent than a mob. This counts for any culture. There are as many beliefs as there are people. But very many people lay back their own beliefs and opinions and adopt a predigested one because it is easier.
Thus we close the Book of Thel.
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