With just a bachelor's in history and no MA/certificate of any kind? To be frank, I think that would not be very helpful for getting a job within the field. I'm not sure of the requirements in every state, though, so it might be possible to get in as a high school history teacher with just a BA.

There are also sometimes jobs in smaller, rural museums that only require a BA in history; however, you'd be competing for them with people who have a BA in history plus years of experience, or a master's. Public history in general requires an MA these days; becoming a curator in a larger museum usually requires a PhD, as does a college professorship.

Don't get me wrong, the BA and the critical thinking and writing skills you got while earning it will help you get a number of less specialized jobs outside of the field. But if you want to work in history, you will most likely need a second degree.