The Department of Defense has a budget of $751.5 billion and $751.4 billion for 2014 and 2015 respectively which is more than the next 10 highest countries in defense spending COMBINED. Lowering the budget to $500 billion per year would save approximately $250 billion per year and would still far exceed any other country's defense spending.
The United States military does NOT have to take on the rest of the world and the money saved could be used to pay off the interest on the national debt or for another more beneficial use to society than war.