Answer:
Every major advance in agriculture has allowed global population to increase. Early farmers could settle down to a steady food supply. Irrigation, the ability to clear large swaths of land for farming efficiently, and the development of farm machines powered by fossil fuels allowed people to grow more food and transport it to where it was needed.
Apparently, all of the names on the map are Irish, so the map suggests that Irish immigrants may take over the United States by the 1900s.
You may well be right about people's fears that immigrants, lots of them from Ireland, would overrun the country. Look up when the potato famine was, though. The map may be from the early 1900s, but, if so, not about the potato famine in Ireland.
Food, Clothing, and medical attention. The slaves first needed care then places to live and work to make money.
The English army relied on archers armed with longbows. Arrows fired from longbows flew farther, faster, and more accurately than those fired from French crossbows.
It helps you better understand the orgins, or the reasons for which the author chose to make something happen, or chose the setting. There are quite a few reasons why it's important. Mostly, it allows a better understanding of why the author chose what they did for the story
