The economy.
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Answer:
The assassination of Franz Ferdinand stoked old tensions beyond the Balkans. The crisis spread as other powers pledged support for either Austria or Serbia. Austria knew that conflict with Serbia would likely involve Russia, which saw itself as Serbia's protector.
There were numerous reasons for the boom of industrialization in the United States. There were many natural resources and America was growing as a whole, which caused more demand for jobs and items.
While the population grew in the United States, there was more demand for jobs, and more items needed to be made and produced. There were now railroads and transportation systems, which made it easier to transport people and items across large distances. This made it even easier for transportation to flourish, as people, resources, and the items being produced could now be sent around, traded, and sold with other people and states.
Being a factory worker in the North was very common, as the South still focused on agriculture, it was mostly the North that had the industries and factories which harbored jobs.
