Because of the Korean War. In the 1950s, there was a war between capitalist South Korea and communist North Korea. The U.S. fought in the war on the side of South Korea, so now North Korea blames the U.S. for all its problems.
"Accept our bank or be the enemy."
Technically, North Korea isn't our enemy... they just hate us, and the feeling is generally mutual. South Korea on the other hand, is our close ally. America and South Korea even conduct routine military training operations in South Korea.
South Korea
YES
The USS Pueblo, captured by North Korea in 1968.
Most probably, the threats are an excuse to keep North Korea's people united against aforeign enemy so that they won't rebel against their government.
No. The US leads the world in enforcing sanctions against North Korea.
North Korea attacked South Korea.
No North Korea is a humanitarian nightmare.
There are several countries which are seen as an enemy of the US. The list includes China, North Korea, Iran, Russia, Iraq, Afghanistan, Syria, and Pakistan.
Yes North Korea does not like the US mainly because of the country's involvement in the Korean War between North and South Korea.
Yes the US is known as the American Empire to North Korea.