If you live in a remote place that's under attack by an upstart band of thieves, start a militia. A militia is a band of civilians trained to do army type business, without officially joining the army.
Militia comes from mīlet-, Latin for "soldier," but the word now refers to a band of fighters who aren't officially soldiers. Sometimes militias add on to regular army forces, like the citizen's militias who fought alongside regular troops in the Revolutionary War. But you'll frequently hear militia if you're listening to news about dangerously violent parts of the world where, instead of voting for change, groups form militias and fight for political power. It's also a verb: to militia.