The immediate cause of World War I that made the aforementioned items come into play (alliances, imperialism, militarism, nationalism) was the assassination of Archduke Franz Ferdinand of Austria-Hungary. In June 1914, a Serbian-nationalist terrorist group called the Black Hand sent groups to assassinate the Archduke. Hope this helps, plus this was the main reason why it happened plus if you see a link other people offer for the answer don’t put it in the web, I tested it out I got a virus. Anyways hope this helps!
That would be productivity.
It was the year 1798 that Thomas Malthus predicted that the humanity would be met with mass starvation. His prediction was based on an assumption that human population would far exceed the means of producing food and that we just would not be able to produce enough food for everyone. But the technological advancement and the advanced farming techniques allowed us to increase productivity and thus avert this prediction.
He does this to emphasize the wrong-doing and to show that there are a plethora of reasons.
Hope this helps!