In five to seven sentences, summarize your understanding of how the united states is changing in late 1900s to early 2000s.

The United States was subject to immense cultural and technological changes throughout the 20th century. In the first half, the consolidation of the western states occurred as a result of the vast migration of citizens who moved there in search of lands and economic prosperity. This prompted a high demand for numerous resources which fuelled industrialization in the country at that time. The second half saw the arrival of the term "The American Dream", as the middle class was bigger than ever before, benefitted from manufacturing jobs which led them to have more economic power and a better quality of life. Towards the end of the century, exponential growth in technological developments and globalization shifted the social landscape, as the once strong middle class, lost ground as thousands of job went overseas to places where labor was cheaper. It also saw the immense growth of immigrants from Latin America, which ended up forming an important ethnical group among the population of the country.

the correct answer is:   the domino theory states that if one country in a region came under the influence of communism, then the surrounding countries would follow in a domino effect.