I'm pretty sure it was a man made law called the 19th amendment. Not so sure it was a great idea either. It seems I read an article several months ago claiming that all the Democrat Presidents have been elected on the basis of Women's votes. Take out the Women's votes, and some of our Worst Presidents wouldn't have been elected.
Did man made law give people equal treatment under the law, or is equal treatment under the law a right that has always existed under natural law?
Not the way the founders practiced it. They obviously believed in equal treatment under the law for people whom they regarded as peers. Slaves and Indians are examples of people whom they did not regard as equals.
Not all agreed with this assessment. Dr. David Ramsey was believed to have lost his bid for the South Carolina Congress seat (to William Loughton Smith) because he was openly advocating the abolishment of Slavery. Not a very popular stand in Slave owning South Carolina.
You may argue that equality under the law is "natural law", but the founders wouldn't have agreed with you in the broadness of your definition as to whom it applied.
Do men have a natural right to keep and bear arms under natural law or is that man made law under the 2nd amendment?