Where can I find a summary of historical spending of the US federal government?
I am not interested in budgets, I am interested in knowing what was actually spent.
You might consider getting in touch with the Data Lab at the Treasury Department, they're actively working on the USA Spending site and also the gov spending data. They might have a good sense of where you can look and would likely be interested in what you are hoping to do with the data.
I know that at least at one point they had data dating back to at least 2000 on their site, because the company I work for, Enigma, has made use of it. (You can see some of that on our public data site, Enigma Public.)
Disclosure: As stated above, I work for Enigma.
There's alot of "data" the government releases in many different formats - it feels like a maze at times. I found a few interesting links for you which I left below.
Some of them get specific, some of them..."miscellaneous." Lots of different reports for different things.
There appears to be alot to wade through; except for the very last suggestion/link I found (which admittedly isn't very historical).
Hope this helps:
Here's a news feed for it: https://www.federalreserve.gov/feeds/z1.html#2090
Or this with a bit of poking around: https://www.usaspending.gov
I poked around and found this: https://www.usaspending.gov/#/download_center/custom_account_data
Selected Federal Account radio button, all agencies, account breakdown by program activity and class, and got a pretty thorough csv breakdown (45,000 rows). Apparently it doesn't go back prior 2017 though.
Pretty interesting actually.