You could do worse than make a proposal to Helion for their series 'From Reason to Revolution' - see http://www.helion.co.uk/browse-title-series-more/reason-to-revolution-1721-1815.html

They welcome submissions from new authors and I have found Andrew Bamford to be very helpful and supportive.

Good luck whatever you decide to do - it's even harder than you think when you start - at least that's how I've found working on my first book, even with Andrew's help.

Regards

Paul