Your text needs to synthesize your research in support of your own argument; it should not be a patchwork of quotations, paraphrases, and summaries from other people. You need a rhetorical stance that represents you as the author. If you cite too many sources, your own voice will disappear, a problem the following passage demonstrates:
The United States is one of the countries with the most rapid population growth. In fact, rapid population increase has been a “prominent feature of American life since the founding of the republic” (Day 31). In the past, the cause of the high rate of population growth was the combination of large-scale immigration and a high birth rate. As Day notes, “Two facts stand out in the demographic history of the United States: first, the single position as a receiver of immigrants; second, our high rate of growth from natural increase” (31).
Nevertheless, American population density is not as high as in most European countries. Day points out that the Netherlands, with a density of 906 persons per square mile, is more crowded than even the most densely populated American states (33).