Religion is a man-made construct for those with perceived authority to control and manipulate the general public. Regardless of the type of religion, it is used as a means to exert control over the general public to conform to the rules of that society. Religion uses fear as a means to rally people in support of those that have the power in any given society. It is the cause of just about every war and human failure. Religion creates division among all people. If there were no religion, people would realize that we are all looking for the same thing (happiness) and we would have the chance to be accepting of other cultures.
It is a sad fact that religion does cause a lot of conflict in the world and has done throughout history. During the European wars of religion which lasted roughly from 1524 to 1653 numerous wars were though mostly due to religious rivalries. One of these wars lasted up to 80 years. Even in modern days religion cusses conflict. Although not directly responsible for such conflicts, the Syrian Civil War is largely tied up with religious divisions with Shiite Muslims fighting on the side of Assad and Sunni Muslims comprising of most of the rebellion.
In recent British history the Trouble in Northern Ireland were effectively a religion "war". Although not primarily fought for religious reasons, religion played a very great role. The Republicans fought for a united Ireland, independent of Britain. Most of the Republicans are Catholic, as is most of the population of (the Republic of) Ireland. In the other hand, the Loyalists fought to maintain the union with Britain. They were mostly Protestant as is the state religion of the UK. Even today, after the Troubles are over, in Belfast "peace walls" quite literally prevent Catholics and Protestants from coming into contact.
Other examples of religious violence are religious terrorism, very prevalent in Pakistan and the middle east in general. Also happening occasionally in the West with 9/11 and the Norway Shooting 2011. Israel is surrounded by enemies due to religious differences (Jews vs Muslims).
So yeah, the trouble is religion makes people different and it is very human to dislike anything different. Oh yeah there would sill be war in a world without religion. But it would be a more peaceful world.
The Holy Spirit of God keeps restrained the evil. Once it leaves .... And it will, sooner than later. You will get the answer to that question. You will have it because the conscience of God will be removed from man, and evil will loosed to corrupt in a fuller way. Remember the tragedy in Louisiana when there was only so much food to be had? Remember the mass destruction of stores and properties, the taking of everyone's possessions, by force. The pillaging, plundering, raping. There you have it. You think your emergency stores are yours? Wait till the next disaster and see just how fast your property becomes the proerty of the strongest .... Oh yes but you have a gun? See how much use that gun is when a MOB attacks and TAKES what they want. You can only pull the trigger so fast, and mobs tend to be greater than just a few people, and OH yeah Hiliary Clinton MEANS to TAKE those GUNS your depending on isn't she?
While religion is the cause of some of the conflict in the world, it is not the cause of all. Many people/groups use religion as an excuse to condone fighting, violence, conflict, war, etc.
The way I see it there are several reasons as to why war, conflict, etc. occurs - religion, greed, love (if you believe the events of Troy), lust for power, rising up against oppression and injustice, to make a change, to make a better society, hate, to eradicate something, etc. Fighting and conflict are what could be called a part of the 'human disease' and religion is not the only reason it occurs.
That is not to say if all religion were removed from the world that all conflict would stop and the world would be more peaceful, there is always the possibility that could happen. But what is more likely is that removing religion will only make a small dint in the bid for world peace.
A religion is a set of beliefs that explain how the universe was created and how logic is set up for us, and where we fit in existence. This brings faith into the human life, but the fact that there are multiple religions is what can lead to a warlike attitude in humans. Catholics, Presbyterians, Muslims, atheists, Buddhists, Hinduists Jainists, candoble, and many other groups all have different views of how the world and the universe was created. All of them are based (loosly) on logic and the most logical view of its creators. But how is this different from the different countries on this earth? Or the different football (soccer) teams that compete with each other, or even us debaters who are testing each other to get the best answer to a question that we have? It would just be another variable dividing us. If people had no belief in anything before the present moment, literature would stop printing, new ideas would run out, people would wonder why they even had to work in the first place, and innovation would reverse. Religion, theistic or not, offers the different layers of reasoning and experience that we need to propel us farther out in life. I am not saying religion induces peace, although some use it that way, i am just saying success and cooperation need reasons, and those are offered by religion.
I think you could remove religion from the world and within days we will have found something else to fight about. I think some nations are just naturally a "fighting people" and they will always have a reason to fight or an honor to defend. Anything that makes people different can be a cause for war, whether it is religion, race, ideology, or politics.
Despite what many people believe religion is not the cause of war. Although countries with differing religions may be at war with each other that does not mean that religion is the root cause. Religion often gives people peace during times of strife and therefore I believe the removal of that peace would actually cause more wars.
If religion were removed from the world, the world would not be more peaceful. I believe if this were to magically happen you may see peace in weird places no one has every seen before. Namely the Middle East. However, there's no guarantee of that. Secondly, religion has provided the human race with a lot of moral and ethical values. If those were gone larger parts of the population would be greedy and self-serving, so overall tensions would increase.
I do not think that a world without religion would be more peaceful than a world with religion. I think that if there were no religion, the world would still have wars. But instead of religion, people on Earth would use other reasons to wage wars against other people in the planet.