About 1,500 miles separate Houston, Texas from Ogden, Utah.
During World War I, 116,516 US soldiers were killed and 204,002 were wounded. If you add those two numbers together, the total number of US soldiers killed or wounded was 320,518.
You can represent that as a fraction of the current population of Chicago like this:

For simplicity's sake (since I assume the Chicago population number is an estimate), let's round the number of soldiers killed or wounded down to 300,000. That would look like this:

We can simplify that down a lot by dividing the number of soldiers and the number of Chicagoans by the least common denominator of 300,000. That would give us this fraction:

So for every 1 US soldier killed or wounded in World War I, there are 10 Chicagoans living in the city today.
I would say that one assumption is the superiority of Europeans over Africans: their belief that somehow they had the right to enslave other people.
This could be connected to their racism (they thought the same of native Americans and there was a discussion whether native Americans have souls) or religious feeling of superiority ("pagans are not the same as Christians"...)
This is an example of exchange theory.
In sociology, exchange theory has to do with maximizing benefits while also minimizing costs. When applied to Bill and Cathy's situation, they are taking advantage of each other's skills in order to minimize costs - Bill can cook and Cathy can't (so they can prepare food on their own) and Cathy can repair stuff and Bill can't (so they don't have to get a handyman).