There is no single root of all problems in the world. Greed =, "true belief" in total ystem ideologies, egocentrism, ethnocentrism are all among the major causes.

unrealistic expectations,lack of compassion/apathy.

People. Take people away and my world is awesome.

God and intolerence. The belief that I am right and every one else is wrong.

The human condition. Our thought processes are far less aware / conscious and far sloppier than most people realize, and our emotions rule us. Even the minority of folks who understand logic, logical fallacies, and critical thinking, under-utilize it (and no, I'm not satisfied with my utilization, either).

Whatever hope I have for humanity is based on the slowly (hopefully, not TOO slowly)-improving respect for rational thought and discourse and the erosion of negative systemic influences like religion.

Greed

Human greed and overpopulation.

Religion and oil.

Tribalism

I am beginning to hate myself for this repetative comment, but I believe it to be valid..............

Religeon is the base cause of most of the worlds atrocities carried out over thousands of years.
I make no further comment.

Human greed without a doubt. The buybull said "money" as a root of all evil, but I'm sure greed covers that nicely.

A lack of empathy.

The root of all problems... Reality. Important to remember when they think you take too much for granted. No reality, no problems. More reality, more problems. Increase the number of variables and the possibility of complications leading to failure increase. Most success stories are tales of reducing expectations, compartmentalizing, and managed time and resources. Not gifts from above, and not extreme suffering.

Thats easy its humans

I would say it is due to our base animal nature. We are basically no different from our caveman ancestors, and therefore not far removed from apes.

If we look at chimps we see many parallels with ourselves. They are social and political, they can use primitive technology, they possess a language of sorts, they are capable of great compassion to members of their troop, but are also capable of great cruelty to members of other neighbouring troops. They also ‘play favourites’ with some members of their own troop whilst shunning, ostracising or outright bullying others.

Humans simply add greater IQ to the equation, which allows for planning and technology. We can then use this for the greatest acts of kindness, such as charities, disaster relief etc., but can also use it for the greatest acts of cruelty, such as war and genocide.

A lot of this boils down to scarcity - i.e. competition for resources, territory, mates etc. If everyone had everything they needed / wanted then a lot of the conflict should fade away, in theory at least. Prosperous nations, communities etc. where resources are in abundance tend to have less conflict than those where resources are scarce. Wealth inequality is therefore a big problem.

The other main cause is the human tendency to follow leaders, which again stems from our animal ancestry. A chimpanzee troop will follow who they perceive to be the strongest leader, and humans do likewise, only now with our IQ, nations, technology etc. those troop leaders may now be the heads of state. Being perceived as a strong leader does not always equate to being a just and decent human being, often it is the opposite, which is how we get the Hitlers, Stalins and Pol Pots of the world.

How we go about solving these problems is anybodie's guess. Anyone got any ideas?

Stupidity?

I can be wrong, but I believe that ignorance is the main troublemaker. At least in my country.

Inequality.

Be it income, race, religion, colour, creed... If we were all to be equal, a lot of the world's problems would fade away.

A tie between superstition and a lack of basic education.

Life

Quite obviously the root of all evil is square. Quick, the square root of 37? Evil, that.

Religions (plural).

I don't know but I do beleive that the future of humanity is very bright, the population will not exceed 11 billion according to most qualified thinkers on the subject, which means we will never run out of either space or resources. We will continue to marry our techologies to nature (the solar panel is a current, though prototypical example). The poet Kalil Gibran said 'Would that I could gather up your houses into my hand and scatter them like seeds throughout the fields and forests'. With the development of green technologies this will happen and our future descendants will live in an environment that grows ever closer to utopia. In medieval times people thought that religion, or 'God' was at the centre of their lives and the root of all meaning, in the future I think people will look at our attitudes to work and consumption in the same way - as outdated and unenlightened. People's lives will become easier.

A very intersting question. In my observation, death can be the root of all problems. Just imagine if no one has to die. I love John Lennon (he's not the only one).

Ignorance - it breeds selfishness, arrogance, and all other ills. In my humble opinion, of course.