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The United States has the world's largest economy (so far), and the world's most powerful conventional military forces. It spends about as much on national security than the rest of the world combined, and nearly nine times more than the No. 2 power (China). It has several thousand operational nuclear weapons, each substantially more powerful than the bombs that destroyed Hiroshima and Nagasaki in 1945. America is further protected from conventional military attack by two enormous oceanic moats, there no great powers in the Western hemisphere, and it hasn’t been invaded since the War of 1812. (A few southerners may want to challenge that last statement, but I'm not going to...