Baby boomers helped out the economy, birth rates increased and a population growth . More goods and services needed
Religion (Christianity) or the bringing of new items (new animals such as horses and improved weapons)
B - Petroleum
Wood was one of the first energy sources, way before the nineteenth century so you can rule that choice out.
Nuclear Energy is more advanced and closer to the twentieth century so you can also rule that out.
And coal was before petroleum, around mid to late eighteenth century possibly.
Hope this helps!
It was a holy war between Christians and Muslims over the holy land
