Q: What challenges did
immigrants, city dwellers,
land the middle class
experience?

The correct answer to this open question is the following.

Although your question has no context in particular or any specific reference to any moment in history, we can answer it in general terms.

The challenges that immigrants, city dwellers, land the middle class

experienced in times such as the end of the 1800s and the beginning of the 1920s, were the increase in population in the cities, the rise of crime, dirty streets, and noise due to the number of people that came to the larger cities where the factories and industries were located.

Farmers decided to leave the rural areas of America to get jobs in the industries. Thousands if not millions of immigrants arrived in the United States looking for better jobs and a better life for their families.

Some authors called this process of an increasing number of people in the cities "urbanization."

The Industrial Revolution created industries and factories in large American cities, as was the case of Chicago or Nee York City. People accepted low-paid jobs under unhealthy conditions, but that offered a better life than farming in the South.

Another factor was immigration. Thousands of immigrants from Europe and Asia arrived at these cities to offer their families a better way of living. Once in these cities, they had to live in poor and overcrowded spaces because these people were poor also and had no money to invest in better housing.

since most of current immigration into the u.s., both legal and illegal, is coming from latin america. it would be very difficult to imagine or rationalize a country my fellow citizens are trying desperately to flee into, would pose a threat to my prosperity or freedom. since the u.s. has a long history of intervention, but no record of permanent occupation, i would not feel oppression is the main objective.  

the largest free trade nation, along with the largest gdp in the world wanting to expand it's economic policy on us, and including us, could only be positive. the u.s. government has no interest in, or way of simply forcing american culture on us. and has no track record of it. other nations that adopted american social culture, or "americanization" did so voluntarily, mainly through the choice of allowing american businesses and u.s. citizens to come into their nations, as free operatives.