Answer:
B. The emergence of industry in cities
Step-by-step explanation:
Why no one moved south
First off its important to note all the problems the south faced after the major loss. For one, 20 percent of the state's budget was spent on artificial limbs for the veterans. It may not sound like a lot but that is lot of money. This also resulted in the economy being ravaged. For example, property values collapsed and were sold for a tenth of what they would have been sold for before the war, confederate money was practically worthless and tens of thousands of horses and agricultural tools were destroyed. So no one wanted to travel to the south.
Why everyone moved north
While the south was practically suffering from their loss, the north had quite the opposite effect. The win boosted the northern economy’s industrial development, commercial agriculture and also strengthened the republican party. The homestead act was passed which enabled landless people to have an opportunity at owning land(over billions of acres were offered). The land resulted in cities being built. Not only that but the Union(north) spent a few millions on military efforts so that new industries had been created to meet the needs for weapons, uniforms, food, equipment, etc.
In summary we can say that the north experienced more availability in land and more job opportunities due to industries being created to meet military needs. This led to the emergence of cities.
So we can say that the emergence of industry in cities resulted in immigrants migrating to the north.
Why the other answers are incorrect.
Although the passage of the homestead act contributed partially to migration it was not the main reason people migrated north. It only enabled the availability of land and did not necessarily show how cities were emerging after the war which is the main reason for migration. i.e. immigrants moved primarily for the opportunities in the cities rather than land as many of them did not operate plantations.
The printing industry was around way before the war and is practically irrelevant to why people migrated north.
The completion of the transcontinental railroad was one small event that led the development of industries as it made travel and trade faster. As immigrants were attracted to the emergence of the cities rather than what led to the emergence of the cities, this cannot be the answer.