This is only partially true. 250 years ago the people of North America were under the control of the British crown. We fought a war to be free of the king's tyrannical rule -- and won our independence. Shortly thereafter the US Constitution was written, which included the Second Amendment...
"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
Clearly this was written so that a disciplined force -- a well regulated militia, not a bunch of undisciplined "yahoos" -- would be maintained to prevent an armed hostile takeover, thereby securing a free state. This means a police force and/or a standing army.
Anyone who claims that it means that every citizen can be armed and shoot whomever they think is dangerous and/or in the wrong is a total lie. Period.