It’s really not a consistent fraction of GDP, and it’s near a record low right now.
Defense spending was officially 2.7% of GDP in 1999 and that’s roughly where it is today, but that’s really low by historic standards. It was 4.9% GDP in 2009 in the middle of a war but sat at 8% through the fifties even after the Korean War ended, and hit 11.3% during it.
Holding the country fixed, I think defense spending as a fraction of GDP probably varies less than debt over time? Like, defense spending of course spikes during wars, but so does debt! (Which is indeed how it is often funded.)
Defense spending was officially 2.7% of GDP in 1999 and that’s roughly where it is today, but that’s really low by historic standards. It was 4.9% GDP in 2009 in the middle of a war but sat at 8% through the fifties even after the Korean War ended, and hit 11.3% during it.
https://www.defense.gov/Multimedia/Photos/igphoto/2002099941...
PS: Though this ignores Veterans Affairs spending, but arguably that should be included when people served rather than just when they received care.