The military used to be a significantly larger percentage of the budget than it is now, but it's not because the military is any smaller. It's because spending on retirees is exploding. Nobody really wants to admit this because the reason the costs are exploding is that there are so many more people over retirement age, which also means that there are more voters over retirement age, which makes it politically very difficult to do anything about it. But it's a serious problem -- how are we supposed to sustain spending more than half of the government budget on retirees?

And the DoD and the VA are also considered separately, but let's not pretend they're unrelated. If you have twice as many soldiers today then you need twice the VA budget tomorrow.