1999 to 2016 is the first 16 years of the Millennial generation’s adult life. Prime family formation and childbearing years.
So what happened during those 16 years:
2002: War in Afghanistan
2003: War in Iraq
2002 - 2007: Housing price bubble
2007-2008: Housing bubble collapse, general economic recession
2009 -2016: Slow economic recovery; changes in worker employment patterns and employee benefits.
So, just at the time that the prime cohort for going to college, starting careers, landing that good job, starting families and buying homes, etc. is beginning their adult lives, they take a series of blows that damages all those activities. And, surprise of surprises, in the face of all this uncertainty, they are not having so many babies.
In the meantime, the Baby Boom generation is beginning to “check out” in increasing numbers with the heavy abusers of, well...everything...leading the way. Since the Baby Boom generation is itself a huge bubble moving through the population demographics, you are naturally going to get exaggerated effects.
The proportion of the United States population that is white has been larger in the past than at the present, so you also get a knock on effect from that in the statistics as well.
The question is: Is this trend also reflected in native born Americans of Asian, African, and Hispanic racial heritage as well? The answer is yes.
Here is some information on US fertility rates from Wikipedia:
“The total fertility rate in the US after World War II peaked at about 3.8 children per woman in the late 1950s and by 1999 was at 2 children. The fertility rate of the total US population was just below the replacement level of about 1.9 children per woman in 1979. However, the fertility of the population of the United States is below replacement among those native born, and above replacement among immigrant families, most of whom come to the U.S. from countries with higher fertility than that of the U.S. However, the fertility rates of immigrants to the U.S. have been found to decrease sharply in the second generation, correlating with improved education and income. As of the beginning of 2016, there are 59.8 births per 1,000 women aged 1544; this is the lowest number since records have been kept since 1909.
Here are US population and demography projections from another Wikipedia article:
“A report by the U.S. Census Bureau projects a decrease in the ratio of Whites between 2010 and 2050, from 79.5% to 74.0%. At the same time, Non-Hispanic Whites are projected to no longer make up a majority of the population by 2042, but will remain the largest single ethnic group. In 2050 they will compose 46.3% of the population. Non-Hispanic whites made up 85% of the population in 1960.
The report foresees the Hispanic or Latino population rising from 16% today to 30% by 2050, the Black percentage barely rising from 12.9% to 13.1%, and Asian Americans upping their 4.6% share to 7.8%. The United States had a population of 310 million people in October 2010, and is projected to reach 400 million by 2039 and 439 million in 2050. It is further projected that 82% of the increase in population from 2005 to 2050 will be due to immigrants and their children.
Of the nation’s children in 2050, 62% are expected to be of a minority ethnicity, up from 44% today. Approximately 39% are projected to be Hispanic or Latino (up from 22% in 2008), and 38% are projected to be single-race, non-Hispanic Whites (down from 56% in 2008). Racial and ethnic minorities surpassed non-Hispanic whites as the largest group of American children under 5 years old in 2015
(There are some good tables at the links. BTW, note where all the growth is coming from.)