(CNN) US population growth slowed this decade, partially due to fewer births, more deaths and a decline in international migration to the US.

Newly released population estimates from the US Census Bureau show that the US population grew just 0.48% since July 2018. Growth has slowed every year since 2015.

The US population increased by 19.5 million since April 2010 -- that's about 0.66% per year. Last decade, the population grew an average of 0.97% annually.

Natural increase -- the difference between births and deaths in the US -- dropped to 957,000 in 2019 -- the first time in at least 40 years that the natural increased dropped below 1 million.

40% of the US population is concentrated in the South, the most populous region in the US and the one that saw the largest growth. Between 2018 and 2019, more than 1 million people moved into the South -- just as more people moved out of the northeastern US.

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