During the 1950s, an increase in the number of marriages and births fueled a demand for housing.
People who was born in the 1950s were known as the baby boomers. The increasing number of marrieages and births in population of post-World War II led to an increase in the demand for housing and gave rise to higher density cities.
By the 1970s, the United States economy had grown by leaps and bounds and was by far the largest economy in the world.
Companies sell stock so they can raise capital.
So the company can afford new equipment, developing new markets, etc..
The trans-continental railroad was completed around this time, so not only did train travel change, but was innovated so that a train could take you anywhere across the US.
It was primarily" "high mountain ranges" that was the physical barrier that helped separate ancient China from Southeast Asia, since these were very difficult to traverse. <span />