Our research shows that if you want to avoid poverty and join the middle class in the United States, you need to complete high school (at a minimum), work full time and marry before you have children. If you do all three, your chances of being poor fall from 12 percent to 2 percent, and your chances of joining the middle class or above rise from 56 to 74 percent. (We define middle class as having an income of at least $50,000 a year for a family of three). Isabel V. Sawhill and Ron Haskins (source, source)
However, that seems to be a bit reductionist. There are many other possible causes of poverty. Some more convincing than others. For example, here’s Montesquieu according to whom people in hot places are simply too lazy to become rich:
In Europe there is a kind of balance between the southern and northern nations. The first have every convenience of life, and few of its wants: the last have many wants, and few conveniences. To one nature has given much, and demands but little; to the other she has given but little, and demands a great deal. The equilibrium is maintained by the laziness of the southern nations, and by the industry and activity which she has given to those in the north. (source)
According to Thomas Malthus, poverty is caused by overpopulation. Food and other resources are limited, and a population growth that exceeds a certain pace will inevitably hit a resource ceiling, and will result in decreasing standards of living, poverty, conflict over scarce resources, famine etc.
Max Weber believed that protestant work ethic put protestant nations at an advantage compared to other nations. Certain values, such as the opinion that God will reward those who work hard and save money, or the belief in predestination—getting rich is a sign of God’s approval—make some nations rich and others, that lack these values, poor.
Jeffrey Sachs focuses on geography and weather. In the poorest parts of the world, the soil is nutrient-starved, making it difficult to produce food. Moreover, tropical climates foment disease, particularly malaria. The UK, on the other hand, the country where the Industrial Revolution started, has a fertile soil, a lot of coal, and good waterways.
Daron Acemoglu states that nations are not like children — they are not born rich or poor. Their governments make them that way.
People need incentives to invest and prosper; they need to know that if they work hard, they can make money and actually keep that money. And the key to ensuring those incentives is sound institutions — the rule of law and security and a governing system that offers opportunities to achieve and innovate. … if you wish to fix institutions, you have to fix governments. [People should be able to] enjoy law and order and dependable government services — they can go about their daily activities and jobs without fear for their life or safety or property rights. (source)
There are obviously many more explanations of poverty, both “exotic” and sensible ones. And regarding the latter, it’s extremely difficult to say which ones are more important. Poverty is surely one of the most complex and intractable problems facing humanity. However, if we look at the country that has been most successful in the reduction of poverty – China – then the last quote above seems to be the most convincing one. China still has institutional and legal weaknesses today, but it did start to develop only after it abandoned the follies of the Cultural revolution and communist rule in general, and started to protect property rights and build its government institutions. Which doesn’t mean that institutions are a “silver bullet” solution to the problem of poverty. There’s no such thing, unfortunately.