Why did industrialization lead to the growth of labor unions?

What kind os source would a historian use to get a firsthand account of a past event

The fourteenth amendment how did the action resolve a longstanding conflict in post-civil war america? it defined the process for readmittance of the former confederate states into the united states of america. it ensured the right to vote to all male citizens of the united states, regardless of race, color, or prior servitude. it defined citizenship and related rights for african americans. it abolished slavery in the united states.

Which of the following areas are best suited for livestock ranching