Merely stating the US budget in dollars verses the Russian or Chinese budgets results in an inaccurate comparison. You're comparing a command economy (China) with a open economy in the US. You're comparing a country were workers often go months without being paid (Russia) with the US. You're comparing countries were the average hourly salaries are a tiny fraction of comparable US salaries. "Apples and oranges" doesn't even begin to describe how inadequate such comparisons are.

The US military spends billions each year because we have a pick up a lot of responsibilities that other nations don't have to worry about. For example, a significant portion of our DoD budget goes to help protect Japan and Europe, so they don't have to spend as much money for their own defense. Through the Cold War years, as much as 1/3rd of our annual defense expenditures went to protect Europe. Given the reductions over the past 10 years, I don't know what the current percentage is, but we still have tens of thousands of personnel stationed in Europe. Why?

Our Navy keeps open the sea lanes so other nations don't have to bother. When countries need to deploy troops quickly, they often turn to us because we have the necessary ships and planes to do the job. We could substancially lower our defense spending if other nations paid for their own defense. For a variety of reasons, some good and some obsolete, they don't.