Final answer:
Increased immigration in the 1970s was driven by the need for workers and both push and pull factors, leading to significant population growth in the U.S. While controversial, the proportion of immigrants to the total population was smaller compared to the early 20th century when considering the overall population increase.
Step-by-step explanation:
The reason for increased immigration into the United States during the 1970s was primarily due to the nation's growing need for workers as industrial output increased. This influx of immigrants, coming predominantly from Asia and Mexico, was motivated by both push and pull factors. Push factors are conditions that drive people away from their homeland, like economic troubles or political instability, while pull factors are attractions that draw immigrants to a new country, such as job opportunities and better living conditions.
The effect of increased immigration on the population in the 1970s was significant. The population growth in the United States during this period was largely attributed to these new waves of immigrants. This trend continued into the 1990s and 2000s, although when considering the tripling of the U.S. population over the twentieth century, the proportion of immigrants relative to the total population was smaller compared to the early twentieth century.
Furthermore, the demographic change due to immigration became a controversial issue, leading to increased military and border patrol presence, the sensationalism of immigrant-related crimes by the media, and debates over the impact of immigration on cultural dynamics, wages, government taxes, and spending.