OP was specifically talking about the 20s, 30s, 40s but just to add a complete picture.
Just to add some empiricism to the conversation
Fiscal Year Tariffs/Customs Individual Income Corporate Income Top Marginal Rate Receipts (% GDP)
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1928 14.0% (approx) DNF DNF 25.0% DNF
1935 8.4% 14.6% 14.7% 63.0% 5.1%
1940 6.1% 13.6% 18.3% 81.1% 6.7%
1944 0.9% 45.0% 33.9% 94.0% 20.5%
1952 1.2% (approx) 42.2% 32.1% 92.0% 19.0%
1960 1.3% (approx) 42.0% 23.0% 91.0% 17.8%
1970 1.1% (approx) 46.0% 18.0% 71.8% 17.9%
1980 0.8% (approx) 47.0% 12.0% 70.0% 18.9%
1990 1.3% (approx) 45.0% 9.0% 28.0% 17.8%
2000 1.1% (approx) 49.0% 11.0% 39.6% 20.0%
2010 1.2% (approx) 41.0% 9.0% 35.0% 14.6%
2015 1.3% (approx) 47.0% 10.0% 39.6% 17.6%
2019 2.0% (approx) 50.0% 7.0% 37.0% 16.3%
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DNF=Did not find
- Tariffs fell from ≈14% of receipts in 1928 to <1% by WWII -> income taxes replaced trade duties.
- Individual income taxes overtook all other sources after 1943
- Corporate shares peaked during war mobilization (~⅓ of revenue in 1944–52).
- Top marginal tax rate was surprisingly not too corrilated to government revenue.
(REALLY wish HN did basic markdown formatting)