Answer:
Not a lot of context in the question but I'll assume that this is taking place around 1780s.
1.America just showed to the world that they were not just an underdog by beating the largest Kingdom in the world at that time, (British empire).
2. Since the country was new there was many open fields for farmers or store owners that big cities like London didn't have.
3. There was usually a monarchy which made the poor stay poor and the rich stay rich, which a poor person can see America as a second chance.
4. America had voting for leaders which was radical at the time.
These are some basic examples that I came up with. I would recommend you take this as points to base your response off of and not just copy it.