Time Stop

I went back a moment, but couldn't stop the bullet.

So I went back an hour, but couldn't stop the shooter.

So I went back a week, but couldn't stop the gun sale.

So I went back a month, but couldn't stop the bullets manufacturing.

So I went back a year, but I couldn't stop the misunderstanding.

So I went back a decade, but I couldn't stop the career path.

So I went back a century, but I couldn't stop the immigration.

So I went back a millennium, and just started shooting until the reason why vanished by temporal changes.