Over half of the current population of the world lives in countries which have below the 2.1 replacement rate (especially the U.S., Europe, China and India). The U.S. fertility rate of 1.64 was last at replacement rate in 2007, and today we are dependent on recent immigrants, who currently do not likely have a higher fertility rate of native born persons but who are more of child bearing age. Asian countries have negligible immigration.

The biggest exception to this trend is Sub-Saharan Africa. Nigeria is slated to be the third most populous country in 2100.

I have posted here on efforts of countries to increase their low fertility rate, especially Hungary. Here is a passage from a 2020 WSJ article which cites South Korea, Russia, Singapore and Sweden:

South Korea spent billions of dollars on low-interest home loans and cash grants to parents to encourage couples to marry and procreate, but its fertility rate has sunk to record lows. In the mid 2000s, Russian fertility rose from post-Soviet lows on the back of grants and tax breaks for parents, but it has fallen again in recent years.

In a recent email to The Wall Street Journal, Singapore’s government cited increases in Denmark and Sweden in the 1980s and early 2000s as evidence that government intervention can help. It linked the uptick to state support for child care and family-friendly workplace policies. But both nations have seen their fertility rates slip. In 2018, Swedish-born mothers had fewer babies than any year since 2002 and immigrants—who tend to have more children—are contributing a rising share of births.