“What causes poverty?” is the wrong question! The real, more useful question we should be asking ourselves is “What causes wealth?” If half the world lives on less than $2 a day, we should naturally ask “What happened to the other half?” From these better questions, we can seek solutions rather than people to blame.
The question “What causes poverty?” seems to imply that wealth is the status quo and poverty is somehow a deviation from that norm. But even a cursory look at history shows this to be a ridiculous premise. History is not the story of how some people become poor but how some people escaped from poverty, the real human norm, and thus became wealthy. I think this a crucial difference of paradigm between the liberal/socialist/communist/Marxist perspective and the conservative/libertarian perspective.
So what causes wealth? Capitalism; free, competitive, and international markets. But that is not all and maybe not even the most important element. Capitalism cannot exist without certain supporting institutions (governmental, financial, social, religious, etc.) and cultural norms that have developed in the West.