Who had the most to gain when african-americans got in trouble for not having a job?

White people.

Explanation:

After civil war, black people had problems to emancipate still. That's why this period is label as 'another form of slavey'. Because african-american from certain job. In that sense, white people were advantage of this situation, because they were able to hire these people.

Another form of gain was the Sharecropping.

supplies had to travel a long distance across water on ships that were often attacked, so they did not reach europe

porter is writing economic history because he is focusing on the cost of developing vaccines.