The U.S. has a nuclear arsenal and is surrounded by the world’s largest oceans. If the military’s sole assignment was defending our country, the chances of anyone seriously attacking us are remote. From Doug Bandow at 19fortyfive.com:

U.S. Marines with Bravo and Charlie Company, 1st Battalion, 9th Marine Regiment, conduct rocket range outside of Camp Leatherneck, Helmand province, Afghanistan, Jan. 31, 2014. The Marines used the range to keep their knowledge sharp on the different weapon systems they use.
Members of Washington, D.C.’s unofficial but bipartisan War Party thrive on bad news. Vladimir Putin is marching on Ukraine. Xi Jinping is reviving the Maoist state and hopes to displace the US from Asia. Iran plans to develop and may use nuclear weapons.
Smaller crises abound. There is chaos and violence everywhere. Lest the new Dark Ages descend, Washington must increase military outlays, intervene more promiscuously, and fight more and bigger wars with greater violence. Not that even then America will be secure. New challenges will impend, and the cycle will repeat. Again and again.
This is not new. At a 2012 hearing of the Senate Armed Services Committee the ever-belligerent Sen. John McCain pressed for war against Syria and cited a lengthy list of supposedly deadly threats to America: al-Qaeda, North Korea, China, Taliban, and Mideast. But that wasn’t all. He added:
“We could continue for some time listing the myriad of other threats facing our Nation, and I am confident we will cover most of them in today’s hearing. What should be clear is that by no objective assessment are the threats to our national security decreasing. To the contrary, they are increasing as the prepared testimonies of our witnesses make vividly clear. So the question that Members of Congress and the members of this committee in particular need to think long and hard about is this: Why, in an international environment of growing uncertainty, risk, and threat, would we choose to add to those risks by making large and misguided cuts to our national defense budget”?
When James R. Clapper, Director of National Intelligence testified, he did not disappoint McCain. Clapper declared: “Earlier this month was the 51st anniversary of my enlistment in the Marine Corps and during my subsequent entire career, I do not recall a more complex and interdependent array of challenges than we face today.” This was not a onetime expostulation but was repeated. At another time he said: “In almost 50 years in intelligence, I don’t remember when we’ve had a more diverse array of threats and crisis situations around the world to deal with and, in the face of that, doing this sequestration thing is quite damaging.”