The three-dimensional graphic below presents answers to some of these questions.
The graphic assembles immigration data compiled by various U.S. government agencies since 1820, when immigration to the U.S. was first officially tracked.
Grouping this data by individual nations and global regions shows the flow of known immigrants to the U.S. from each part of the world.
The most striking feature of this chart is the irregularity of immigration from different nations and regions.
The peaks and valleys in the chart represent immigration waves that occurred at various points in history.
Immigration totals for each country are represented by a series of bars; each bar shows data for one year. You can see the annual volume of immigration by comparing the colors on each bar with the immigration-volume indicator in the upper-right corner of the graphic.
Changes in color to red from green show a growth in immigration. The dark-black horizontal lines on the bars show units of 100,000 people.
The graphic's horizontal scale contains a time line from 1820 to 1993, and places in context major events, such as financial depressions and global wars, that have influenced immigration.
While some events encouraged immigration, others made it difficult: Depressions tightened most job opportunities in the U.S., and global conflicts disrupted transportation routes.
As the graphic shows, there was sometimes a lag between events and their impact on immigration. Notice the delayed effects the two World Wars, which started in 1914 and 1939, had on European immigration.