The US defense budget, as a percentage of GDP, has been cut a huge amount! https://data.worldbank.org/indicator/ms.mil.xpnd.gd.zs?locat...

If you don't think it makes sense to scale it by GDP (though I do), then in real terms it has gone through cycles since 1965, with definite periods of decrease, even though the overall trend is upward: https://www.johnstonsarchive.net/policy/edgraph.html