It's a long story starting from the beginning the English settlers conqured america from red Indians, guns were a requirements just to stay alive and to protect themselves from red indians and other european colonists. Then the civil war made the people especially whites in the south distrust the government as a result of abolition of slavery. It only strengthened gun owners resolve to bear arms. Today it is very unlikely that the American gov't will use military to massacre its own people, but as the american citizens have the rights for more than two centuries, it is extremely difficult to take it away. Just like it is difficult to take away freedom of speech and religion in america, it is difficult to take away right to bear arms as it is included in bill of rights. To amend the constitution it requires 2/3 of members voting in each house and then approved by 38 states. Most southern and Mid west states are gonna reject it so it have no chance in the Congress although I believe most americans support gun bans.