Colt Made Them Equal

"God created men. Colonel Colt made them equal."

- Old frontier saying, quoted by Larry Koller in The Fireside Book of Guns

After ten thousand years the Sealed Evil in a Can is finally free and thinks it's time to Take Over the World (or destroy it. Possibly both.) using its mighty power. With its immunity to swords and arrows, what hope does humanity have of defeating it?

Fortunately for the continued existence of humanity, while its been gone modern arms development has really taken off and the once mighty forces of the supernatural are no match for the power of modern firearms. Even a Ragtag Bunch of Misfits can hope to defeat ancient, world enslaving monsters with access to More Dakka.

Common in Urban Fantasy. Contrast Immune to Bullets.

Literature

 * In Monster Hunter International the two newest members of a group of vampires, a Nazi and a former monster hunter, warn their group that while they've been sleeping modern weapons have made humanity much more dangerous to deal with and they should act with more subtly. Fortunately for humanity, the others don't take their advice and sneer at the might of humanity's "cannons".
 * Word of God for the Harry Potter series is that modern weapons would make short work of wizards, which is a reason for their modern isolation.

Live-Action Television

 * In Buffy the Vampire Slayer a demon that was sealed because it was immune to any weapon "forged" proves no match for a rocket launcher.

Tabletop Games

 * Part of the reason supernatural forces hold their version of The Masquerade now is that modern humanity is more than equipped to bring them down if they know. Even those that have protection from normal bullets will fall quickly to great volumes of them or heavier stuff like explosives. Unfortunately for them the modern age also brought the internet and cell-phone cameras, which make their hiding hard.
 * Which game is this from? "The Masquerade" is a trope, not a work.

Video Games

 * Eternal Darkness many player characters cover two thousand years of history. The early ones tend to die (or live) horribly after their adventures. The ones with guns tend to live, if horribly scarred from their experience. Dr. Lindsey manages to scare off the Centurion lich Pious Augustus through use of shotgun.