Without changing the country's borders?
- No Immigration Acts of 1917 and 1924 (20 to 30 million?)
- Get the U.S. to adopt a policy which, if not explicitly pro-natalist, is highly supportive of something like a UBI for kids and health coverage for kids (CHIP wasn't until the 1990s OTL).
- No Roe v Wade. Abortion will end up legalized state by state over time, but it won't be as available (pre-Roe setting the bar at 28 weeks, the most liberal state was New York at 22 for example, and other states probably won't have it until 15 like is typical in Europe) and it will come later, meaning more babies born and more people generally.
- Have some minor PODs changing US housing policy so that you don't have the cost of living constraints that first started popping up in the late 20th century, meaning people are willing and able to have more kids.
- During the Indochina Refugee Crisis and Vietnam Withdrawal generally, the US adopts a super pro-refugee policy. Any Hoa (Vietnamese Chinese), Catholic, SVA veteran, family of SVA veteran, Hmong, South Vietnamese businessperson, or South Vietnamese public official can get into the US. By 2020 these folks and their descendants in the US number about 20 million. This later translates into a much broader 'victims of communism' Cold War immigration policy that over time means another 10 million immigrants.
OTL the US government stuck the Vietnamese refugees all over the place. Guam, Texas, Louisiana, Kansas, Minnesota, California, etc. It would probably be similar here.
European immigrants would land on the east coast but over time move to other cities in the middle and the west of the country, like OTL.
1. I'd argue the 1924 immigration act was ultimately unnecessary, considering that immigration levels would've crashed in the depression a few years later. However, the U.S. would've gotten a ton of immigration during the Post-WW2 emigration boom from Europe, thus leading to millions more White Americans ITTL.
2. I think something like this would've happened without the postwar Baby Boom. Fertility rates crashed in the Great Depression across the entire western world, and lawmakers would've eventually taken action if they didn't rebound in such a big way after 1945. Alternatively, the Baby Boom could've ended more slowly and not crashed as hard, with the fertility rate settling just above replacement level by the year 2000.
3. Not touching this with a 39 and a half foot pole.
4. Housing is going to be expensive in high-demand cities and especially high demand cities with limited room to expand like San Francisco, but maybe the U.S. develops denser urban areas similar to Pre-WW2 suburbia (look at parts of NYC and Chicago for examples), thus leading to a higher housing supply with less space being taken up by lawns and driveways.
5. I think this would change U.S. politics significantly. If the Vietnamese were invited in en masse during the Nixon and Ford administrations, these Vietnamese Americans would at least be a swing demographic, if not a Republican voting bloc (OTL's Vietnamese Americans are split roughly 50/50 between Democrats and Republicans). This would make the GOP more comfortable with minority voters, showing that they could indeed end up voting Republican, which might lead to them being more successful with Hispanics and other Asians. Hispanics and Asians being 50/50 or even 60/40 Dem/Rep voters would make the Republican base more comfortable with demographic changes, since it wouldn't equal political doom. However, that's probably best left in chat.