The U.S. population is showing signs of recovery from the pandemic after growth hit record low levels last year, and Americans mainly have people from outside of the country to thank for it.

The resident population grew by 0.4% in 2022, the Census Bureau said on Thursday, a rebound from last year when population growth almost flatlined at 0.1%. There are now 333.3 million people living in the U.S., after adding nearly 1.3 million people in the past year.

Part of that population gain comes as there were more births than deaths in the U.S. this year, adding around 245,000 people. The birth rate represents the “largest year-over-year increase in total births since 2007,” Kristie Wilder, a demographer in the Population Division at the Census Bureau, said in a statement.

But while a relatively high birth rate helped, it wasn’t the main reason U.S. population growth returned to normal levels according to the bureau.

The biggest driver was a rebound in people migrating to the U.S.

Net international migration—the number of people moving to the U.S. minus those leaving the country—was the “primary driver of growth” for the population this year, according to the census. Net migration was positive at more than one million people, a 169% leap over the 376,000 population increase due to migration in 2021.