A good concluding paragraph for your outline that summarizes the main ideas and restates the thesis statement is the following:
In conclusion, the migration to the United States is very common because throughout the years this country has been considered as a country where migrants can have better life conditions. However, migration has caused overpopulation in this country, and good opportunities are now limited because of the huge amount of people who are seeking to have them. For this reason, social problems such as crime, poverty, lack of education, and less job opportunities have increased. Unfortunately, the opportunities decrease, and the overpopulation is ruining the quality of life in the country.